It;s 19 here, 18 in quebec, and I think we have all the same issues as everywhere else. I also think by having it at 21 more kids are sneaking off, binging, etc. Plus, 21 is OLD. You can drive, vote, get MARRIED, go to war, and do all the adult things...why not have a drink?
Sending a 19 yo off to University, away from Mommy...he's going to drink, party, etc and not learn how to be responsible with it from parental influence.