Actually, no-one said that martyrs are to get 72 virgins either. If you go to the root of the myth, its origin is a VERY weakly sourced saying attributed to Muhammad via a chain of half a dozen narrators.
And what is said was that the person who got the smallest reward in heaven would get, among a lot of other things, 72 Houri (the word sometimes translated as Virgins, but almost certainly refers to non-human creatures of divine beauty, etc). Keep in mind that this isn't supposed to be what was promised to martyrs, but to those who were able to stop themselves from being such assholes to other people that they barely didn't get tossed into hell.