I am curious if this is just speculation or if you have evidence for this statement? At first it seems reasonable but I am not so confident after you factor in modern medicine and advances in nutrition/diet and discount for stereotyping.
Another quote: "Modern longbows have a useful range up to 180 m (200 yd). A 667 N (150 lbf) Mary Rose replica longbow was able to shoot a 53.6 g (1.9 oz) arrow 328 m (360 yd) and a 95.9 g (3.3 oz) a distance of 249.9 m (272 yd). A flight arrow of a professional archer of Edward III's time would reach 400 yds. It is also well known that no practice range was allowed to be less than 220 yds by order of Henry VIII"
Yes in fact they did spend their whole lives practicing. (From http://en.wikipedia.org/wiki/English_longbow#Training):
"Longbows were very difficult to master because the force required to deliver an arrow through the improving armour of medieval Europe was very high by modern standards ... etons of longbow archers are recognisably deformed, with enlarged left arms and often bone spurs on left wrists, left shoulders and right fingers."
Further:
"It was the difficulty in using the longbow which led various monarchs of England to issue instructions encouraging their ownership and practice, including the Assize of Arms of 1252 and King Edward III's declaration of 1363."
The popularization of the crossbow, in part, was the reduceded need for training. In some areas it also paid better.
This is for shooting at a block of billmen, which does not require much in the way of aim. So long as you aim in roughly the right direction, and get your elevation and draw length mostly right, that's all that's really necessary.
For target shooting, most competent archers will be able to hit a 1m target at 20m >75% of the time, loosing in time with a 12/minute count.
PS: There is something of an arms race with bows, if you use a 100lb bow and your opponents use 80lb bows you can slaughter them before they get into range. (Ignoring wind, and terrain issues.)
If that fails, and someone is anywhere near 20m, you drop your bow and a) draw your own hand weapon, or b) more likely - run. Because if you're up against someone whose primary weapon is a sword, they're likely to be better than you and have more/better armour, so your odds are low. On the other hand, if you're up against a billman, your odds are basically zero.
I only put the accuracy for a 20m target because a) that's what we shoot at for practice in my reenactment group, and b) to demonstrate that most people can aim moderately at that distance while shooting quickly - they're not just pinging arrows off in any direction in order to get the rate of fire up.
As a longbow archer, your primary job is to put as many arrows as possible into a large block of men 200m-300m(-400m?) away before they get to the billmen you're protecting (and who are protecting you.)
Even for commeners they were still often legally required to spend a significant amount of time working on their marshal skills - mainly archery.
http://www.amazon.com/Time-Travelers-Guide-Medieval-England/...
e.g. Here in Scotland there was a time that games like golf and football were officially banned as they were seen to distract men away from military training for the wars with England.
The short answer is that a typical modern person (gamer or no) is much less fit than anybody from the age of melee weapons, let alone knights.
But I don't have smallpox. Or cholera. Or an iodine deficiency, because I live so far from the ocean.
http://www.bbc.co.uk/news/10138060
http://www.stirlingcastle.gov.uk/home/newsevents/bbc2history...
http://www.dailymail.co.uk/news/article-1279306/Face-mystery...