My wife thinks that part of the attraction is she's so accustomed to being better than anybody else that the idea of Anakin, who is capable of overpowering her, is, ahem, part of his sex appeal. I'm not the one to judge how much sex appeal Anakin projects, however! This fits with what I said about the lust angle to their relationship though...
That's funny, my wife thought Amidala just wanted to be his mother. ;^)
-Kevin