The difference lies in how the colonies were administered. i.e whether the colony was extractionist or whether it was intended to be more independent. Colonies in North America, for example, had far fewer valuable natural resources to be exported, whereas in the south there was a relative abundance of gold.

This led to something similar to 'Dutch Disease' in the sense that there was no incentive to grow the Southern colonies and make them self sufficient, as there was such an easy profit to be made.

As a corollary, this mean't that Spanish, French and Portuguese colonies had far less autonomy than British colonies in general, and were run more like businesses than what we'd nowadays consider colonies. Over time those colonies which had more of a focus on economic growth eclipsed those which existed to make cheap profits. Although the above primarily focuses on America, it highlights the colonialist doctrine of the nations involved.

Saying that, by the end of the 18th Century, South America had started to become far more economically powerful than was the case in earlier centuries. If Simon Bolivar had successfully managed to unite Latin America, then perhaps today we'd see a Latin State to rival the USA?

For more information, read Niall Ferguson's "Civilisation: The West and the Rest" http://www.amazon.com/Civilization-West-Rest-Niall-Ferguson/dp/0143122061

I'm not going to pretend to be qualified enough to give an answer outright, however I do think you should qualify or re-word your question. You should consider what types of colonies you're comparing. Settler colonies are going to be extraordinarily different than other colonies which were more of an imperial subjugation of the local populace. All the examples of British colonies being successful that you've given are settler colonies, ignoring the large majority of their colonial empire. Perhaps a better question would be, why do settler colonies seem more successful than other imperial holdings of European powers.

While in general, I'd agree that ex-colonies of the British Empire have fared better than Spanish, French, and Portugese ex-colonies, I think you have to be careful cherry picking the colonies you deem successful.

The US, Australia, New Zealand, and Canada all shared commonalities - they relied heavily on large immigration of European settlers to build up their economies and civil societies, and were administered less as conquests to be exploited but rather an expansion of their society. And to be fair, the French have a lot to do with the territories that eventually became part of Canada and the US as well, so it's not fair to exclude them entirely from their list.

A better point to may be to argue about other colonies that weren't reliant on heavy European immigration and were instead based on local subjugation - and the record is a significantly bigger mixed bag.

Sure, you have the modern Kingdom of Jordan (formerly a British mandate) which has been stable in its recent history compared to say, Lebanon (French). Then again, you have Syria (French) compared to Iraq (British) - neither exactly appealing examples. Egypt may seem like a relatively big success for the region, but then the French had Algeria which has shared a lot of common issues in recent years.

And in some cases, it's too early to say how things will fare. India is frequently cited as a former British subject that has great success, but then again Vietnam - despite having a government type the West isn't happy about - has improved the living conditions of its citizens far better than India has and is still undergoing reforms.

Likewise, another example of being careful with cherry picking is that even within the British colonies, the results vary tremendously. South Africa hasn't had an exactly savory history in the 20th century, but compared to its neighbor Zimbabwe, it looks like a saint. Or Egypt vs. Sudan. And compared to other country's colonies, are those guys really that much better off than Brazil, Argentina, Mexico, Costa Rica, etc.?

USA, Australia, New Zealand and Canada are all immigrant colonies/countries, i.e. the population consists mostly of Europeans and not of natives. European immigrants brought their skills and technologies with them, and so they had an advantage. The only ones of the Spanish, French, and Portuguese colonies with the same high percentage of immigrants might be Argentina and Chile. The reason for this seems to be geographical coincidence: Canada, Australia, New Zealand and the USA were all very thinly populated before the arrival of Europeans.