I'm one of the few dudes that see's this differently probably... A woman dumping a man because he wont commit is not worse than a man dumping a woman because she wont put out. I like sex as much as the next guy, but any dude that dumps you because you aint give it up in 3 months aint worth the time anyway. Believe me, if someone really likes you they will wait however long it takes.
If a person is ready to commit and the other person isn't, that's a legit reason for dumping them. Someone not giving it up in a timely fashion...not so much. But hey whatever, to each there own. The thing is that usually with sex, both people if really attracted to each other in anyway want it and want it asap. So usually you don't get to far with not giving up unless one of them is a virgin or something.