As a woman, I actually agree somewhat with Sir Lance on this, but not on the shorts rolling issue. I consider myself to be a rational person and not a flashy dresser (all of my shirts reach all the way down to the top of my pants, and I do indeed wear a belt if I think my pants slip down a little when I sit, among other decencies), but I DO roll my shorts. For the exact same reason everyone has cited, they're seriously just more comfortable. The elastic doesn't rub against my belly, the shorts don't ride up etc.
In fact, I would say those that roll their shorts (just once, that's reasonable in my mind), are actually being more conservative, because if I buy shorts such that the built-in underwear fits me well (i.e. I wouldn't need to roll my shorts), the legs are so damned short that I feel like one of those British skanks going to the beach on vacation with their 0.5" inseam jean shorts hiked up their crack. So I buy a size up, to cover my butt, and as a result, have to roll my shorts. On the other hand, whenever I am issue shorts with those 3/4 splits, I always pin them closed, because I really don't like my as showing every time a breeze kicks up.
So, basically, yes, often times, we women are slaves to fashion. But hey, looking good feels nice. It doesn't mean we're sluts. I love running and I happen to also love the body that running gave me, and if I fits well in a bikini I can wear it if I please. Please don't try to tell me that guys don't buy clothes they think they look good in, even for running. Seriously... the speed suit? Sure, you can argue the functionality of it, just as we can argue the functionality of rolling shorts, but in the end, I could also argue that guys just know they look hot in them, using every justification you're using, and we'd be having the exact same argument.
Bottom line, some of what we wear is functional, a lot of what we wear is chosen so that we look good, but I just don't see the problem with looking good--it's not the moral equivalent of sleeping around, as much as you'd like to make it out to be.