I don't know if there are limits in any division.
You don't see as many DI teams with a lot of foreigners, but the more successful D1 teams have the 'pick of the litter' and can get the best US players. I have seen D1 rosters with as many as 10-12 foreign players.
I know there are no limits in DII and DIII and obviously there are no limits in the NAIA or schools wouldn't have 25 foreign players.
I think it's good for US players to get to play with and against talented foreigners, but there should be limits. After all, the scholarships are being paid for with American money!
As an aside, there are an awful lot of foreign coaches in our colleges as well. The local school is coached by an Englishman, the nearby DI school is coached by an Austrian, another nearby DII school is coached by a Hispanic (not sure of the nationality) and the team that won our conference (DII) is coached by a central European.
Higher ed soccer programs are definetly fascinated with foreign coaches and players. I think the generation coming up now should have some good coaches with experience that could lead a program.
I am going to agree with you. Actually college soccer is mostly composed of American, along with some foreigners. If you are a young player thats good overseas, there are alot more options than playing for a college team in the US.