I'm kind of torn on this issue.
On the one hand, the statistics do show a drop in alcohol-related traffic accidents in the 18-21 age group.
On the other hand, if you can be told to fight and die for your country, you should be able to drink a beer in it.
A 21yo drinking age is also very difficult to enforce, especially in a college environment. When I was in college, I had plenty of 21+ friends who were willing to buy for me or lend me their ID. I also went to many a fraternity party where you were carded at the door but the pledge tending bar would cheerfully ignore the big black X on your hand.
Maybe a graduated drinking age is the answer. You could bring back the 18yo drinking age for 3.2 beer. Or, I heard a proposal in the UK (where the drinking age is 18) that would allow 16 and 17yos to have a beer or a glass of wine (no hard liquor) at a pub as long as it was with a meal. It would be tough to enforce, though... you could always eat your dinner reallllly slowly...
On a related note, when they raised the drinking age from 18 to 21 in New York, 18-20yos were not grandfathered. I remember seeing news stories where they showed liquor stores jammed with 18-20yos who were stocking up. They interviewed a guy who had just turned 18 and was stocking up on all the booze he wanted to get through the next three years...