Interesting read. I definitely concur about the general attitude in America towards underage drinking is based off fear, that children, teens, and college-aged adults aren't going to be responsible drinkers and/or they won't respect alcohol to the point they don't know when enough is enough.
From personal experience, my father was pragmatic about me drinking in my high school days just because it was expected that somehow, some way, there was going to be booze at the party, but I reckon it was also trust in me to be responsible. My mother being assimilated to the cultural perception of alcohol was extremely averse to me drinking, but in the end, caved in and eventually got her blessing to go to such wild parties. Aside from a few times, I wasn't drunk all that much in high school whereas my friends were flat out plastered as they drunk simply to be drunk. However, in my first couple of years in college, I wound up being more drunk (as depression set in), but my time abroad in France actually gave me greater appreciation of alcohol in general and even though I spent many a weekend drunk, I just drink (like Coppermine) for the appreciation of a well-brewed beer.
As far as peer pressure to drink at an early age goes, I think the pressure is greater in Europe (especially in the UK) than it is in America, interestingly enough. It's not so much that you're urged to have a few drinks at 10 or 12 years old (i.e. "to look cool"), but it's the expected norm, like a rite of passage, so to speak. At a European wedding, it's definitely OK to have a beer or two, and/or a glass of wine or two, and the bartender behind the private bar wouldn't mind. The inferred rationale behind it is that the parents/guardians are solely responsible for their children's intake of alcohol and not on the party hosting the occasion.
This doesn't mean that adolescents in Europe aren't as likely to engage in risky behavior because quite frankly, I know many a friend back there who has in their high school days and even to the present. However, I think you see less alcoholic abuse and incidents of drunken driving not just because there's lesser fascination on the substance of alcohol in and of itself, but because the laws are extremely strict on DUI incidents than they are generally here in the States. Because mass transportation is easily accessible from the biggest of metropolises in Europe to the smallest towns, not only is it efficient to get around town this way, but the network is so extensive you can get around just about anywhere. I don't think this is the main factor on this trend (as it doesn't nail completely why alcohol abuse is relatively lower than in America), but I think it's one of them.