Personally, I wouldn't trust Gladwell's or Robb's books any further than I could throw them. In general, you should distrust any work of history that is pitched as a "personal journey" by the author - what Robb calls "four years in the library" supplemented by "fourteen thousand miles in the saddle [of a bicycle]" - or that manages to uncover a "secret history" heretofore ignored by academics (for the record, Gavin Menzies uses the same tactic in his ill-conceived Chinese pseudohistory 1421). However, this feeds into a larger issue with The Discovery of France that's relevant to your own question.

If you read reviews of Robb's work in academic journals (which are universally unflattering), there are quite a few criticisms that pop up frequently regarding The Discovery of France. The one concerning the "winter hibernation" of French peasants relates to a major shortfall of the book in confusing representations with reality. Time and again, Robb will repeat 19th-century myths and literary creations regarding France as if they were truth, uncritically using them to paint a picture of a romanticized France that has long since been rejected by historians. To quote David Bell's review of the book in New Republic:

As for the winter “hibernation,” it not only plays down the considerable work that French peasants did in the winter repairing tools, making clothes, tending to animals, and traveling outside their villages as hired laborers; more importantly, it also ignores the crucial phenomenon of proto-industrialization. As historians such as Liana Vardi have shown, in some areas of northern France already in the eighteenth century a majority of rural households had abandoned subsistence farming to become weavers, producing textiles on a fairly large scale as part of extensive commercial networks based in the cities.

The book Bell is referencing is Liana Vardi's The Land and the Loom: Peasants and Profit in Northern France, 1680-1800, an excellent work that does a lot to dispel myths about the early modern French peasantry. By contrast, if you've ever read any of the anthropological tracts about "pre-modern" France produced in the late 19th and early 20th centuries, Robb's book reads a lot like them. I'm guessing the assertion about winter hibernation was something he picked up in a similar text intending to contrast the "backwardness" of the French peasantry with the "modern" and repeated without critically examining the claim.

Most of the reviews I've read criticize the book as an ahistorical, anti-modern polemic, and after reading it I tend to agree. You can read another good review of the book here (on H-France) by historian Steven Kale.

I've never read this, but it actually could be true in some parts of France during harsh winters indeed.

Despite the fact that life was very much slowing down during winters, there were things to do for the peasants. Some would actually take care of some works in they had a small workshop at/near their home ( a workshop could have a simple table and some tools ) to make shoes, repair some tools for the coming season,...Etc

Winter was also the time of a strong community sense, especially in villages. There were evenings spent in groups to tale tales and play some games at the local inn. Benoît Garnot said in his book Société, cultures et genres de vie dans la France moderne that :

"Even if the vast majority of the people is illiterate, the book has an important place in the popular society. THose who cannot read enjoy the communal/public reading during the long winter evenings. The " Blue Library ", mostly aiming poor people is the most famous popular collection of books. "

That said, the XVIIIth century was a century with a lot of famine, often due to terrible winters. 1709 might be the most well known, which also affected other European countries. It was caused by war and also very harsh winters. There has been one catastrophic winter in the 1760s as well ( can't remember the year ) added to poor summer and bad harvests and all this caused popular revolts.

So, I'd that life was not shut down during winters. It was slower and more difficult but the people through centuries learned to live with it and find things to do. And there was work to do as well, not as much but still. Also, that's a bit off but in the cities, winters were the best time for gamblers and other money games. Authorities had a difficult times regulating the lotteries and other games involving money where and when they were allowed. Prostitution was also very important during winters and an inferno for the police and authorities to control.

Source : Benoit Garnot

Georges d'Avenel, Paysans et ouvriers depuis sept siècles ( Peasants and workers since seven centuries ).

The New York Times did an article on this behavior, apparently it was fairly common in Pskov Russia where the winters are much more frequently brutal.

http://www.nytimes.com/2007/11/25/opinion/25robb.html

The article I note is written by Graham Robb, so that isn't shedding any new source on the matter... this article has a link to the BMJ article written in 1900 (reprinted in 2000, and behind the BMJ Paywall)

http://inhumanexperiment.blogspot.com/2010/03/curious-case-of-human-hibernation.html

I found the text of the article, it isn't very lengthy:

A Practice closely akin to hibernation is said to be general among Russian peasants in the Pskov Government, where food is scanty to a degree almost equivalent to chronic famine. Not having provisions enough to carry them through the whole year, they adopt the economical expedient of spending one half of it in sleep. This custom has existed among them from time immemorial. At the first fall of snow the whole family gathers round the stove, lies down, ceases to wrestle with the problems of human existence, and quietly goes to sleep. Once a day every one wakes up to eat a piece of hard bread, of which an amount sufficient to last six months has providently been baked in the previous autumn. When the bread has been washed down with a draught of water, everyone goes to sleep again. The members of the family take it in turn to watch and keep the fire alight. After six months of this reposeful existence the family wakes up, shakes itself, goes out to see if the grass is growing, and by-and-by sets to work at summer tasks. The country remains comparatively lively till the following winter, when again all signs of life disappear and all is silent, except we presume for the snores of the sleepers. This winter sleep is called lotska. These simple folk evidently come within the terms of Touchstone's definition of a natural philosopher; and many whose lot is cast in places where men are breathless with the fierce race for power or glory or wealth would doubtless be disposed to say of them, 0 fortunatos nimium sua si bona norint! In addition to the economic advantages of hibernation, the mere thought of a sleep which knits up the ravelled sleeve of care for half a year on end is calculated to fill our harassed souls with envy. We, doomed to dwell here where men sit and hear each other groan, can scarce imagine what it must be for six whole months out of the twelve to be in the state of Nirvana longed for by Eastern sages, free from the stress of life, from the need to labour, from the multitudinous burdens, anxieties, and vexations of existence. (BMJ 1900:i;1554.)

The latin above says: "O how extremely happy could farmers be, if only they would count their blessings!"

It is originally from Virgil, Georgics II, but more recently from Patrick O'Brian's 1972 novel "Post Captain"

Touchstone, mentioned above, is from Shakespeare's "As You Like It"