Yeah, that's actually a good point. I think men often LIKE to pay for things for their girlfriends, partly out of an attempt to impress, and partly because that's how they feel it should be? I dunno, I know I actually get pleasure out of spending money on my girlfriend. It's fun and enjoyable and I think that part of it makes it hard for straight women to redress the balance, perhaps, because the sexual stereotypes are in place.
So instead they replace this with trying extra hard to look good to make up for the fact he's always paying for stuff, which then in turn promulgates the theory that women use sex to get men to buy them stuff. There's little doubt women use sex to get what they want (and I think most women would agree with this) and know it's a very useful tool to manipulate a man. Men can't do this as sex IS what we want. So perhaps we pay for lavish gifts because we think if she thinks she's going to get more, she'll put out more often. I wouldn't go so far as to say women DO put out more often for gifts, however.
I definitely think it's interesting and I wasn't being shallow or critical of women.