While it is illegal for gambling operators to offer their services to US citizens, it is not illegal for US citizens to accept their services.
If you like to gamble online, fortunately there are many operators that accept US players, despite the legislative dangers.
The reason you CAN have a mathmatical edge over the casino is not because of any crazy strategy, but because of the bonuses they offer. They offer these bonuses because of the extreme competition that exists between online casinos. The
best casino generally don't take US players.