So, this isn't exactly scientific, but it seems that when i look at photos of men from the WW1 era and prior, in group photos of soldiers almost all of them have very respectable facial hair. You can easily find a group of five or six guys with thick moustaches.

But it seems like for me that if every man i knew stopped shaving for a year, there would be far fewer people who would have anything more than some scattered growth. only a small fraction of men i know are capable of growing in the type of facial hair you see in pictures from a hundred years ago.

example: http://www.archives.gov/research/military/civil-war/photos/images/civil-war-030.jpg