Things may be different in North America, but here in Europe the gate time printed on boarding passes is the time they start boarding, not the time the gate closes. They like to have everybody at the gate at the time printed on the boarding pass, but that doesn't mean they won't let you on if you're not.

For long-haul flights the gate time can be as much as an hour before departure (I think I may even have seen 90 minutes). If you arrive at the gate half an hour before your long-haul flight you will find that they have just about finished boarding the long line of people that was there half an hour earlier, and you walk straight through. Of course if everybody were to turn up at the gate at the last minute they wouldn't get the flight off on time...