I don't get it. I lived in countries where there was no drinking age, period. Kids were very responsible there because they grew up with it and saw it was part of the family meal (wine, etc.). When I was 10 I could have had wine but I didn't want it and there was nothing "cool" about being able to drink it. I never saw kids binge drinking or drunk for that matter while abroad, then I came to the USA and it was completely out of control. Frat parties were held almost every night and people were passing out from drinking too much. I could not understand what all the fuss was about.
I say do away with any limit, maybe I'm being too optimistic but I think American children can be as mature as their European peers (after all we started from there).