You can buy plenty of raw milk cheeses in America, but the law requires that it be aged for something like 30 days before sale. It's not a problem for most cheeses, most actually benefit from sitting around for a month or so.

That being said, there isn't much in the way of actual scientific evidence that raw milk cheese makes much of a difference; often the milk is heated enough in the cheese making process to induce similar changes in the structure of the milk.

Far as I can tell, raw milk is more expensive, so more expensive cheeses use raw milk.