It really does depend on the individual person. I don't think most men have relationships to have sex, though the ones that do tend to make those of the male gender seem cliche. Women usually have sex only when they're in relationships because they seem to need an emotional connection more often.
Comparing both males and females I think men find it easier to have casual sex, although I believe people who do are relatively rare.
And then there are those women who become sexual with perfect strangers hoping to get into relationships, (I have a friend just like that) but they never get anywhere, and I'd like to say that the majority of women wouldn't think twice about doing something so sad and desperate.