part of the reason is that most of these guys don't go to college and that's where you would learn to be proficient in a foreign language in the US. There's one, ONE player in the top 100 now who graduated college (and that's pretty much the only reason why I'm a Brian Vahaly fan).
At Harvard, I'm sure Blake took a foreign language.
Americans not being able to speak other languages has always been one of my pet peeves.
John Isner now.
Judging from experience, you don't need to be all that good at a language to graduate college, though.
Anyway, when I found out Safin spoke Spanish in addition to Russian (my two favorite languages other than my native tongue), my interest in him definitely grew exponentially...