I think the reason we see more males tickled in mainstream television and movies is that, for most people, tickling is kind of a slapstick, ridiculous thing, and men are much more often the "victims" in slapstick comedy than women are. I think it bothers us, culturally, to see women as the victims of violence (as it should), and that kind of carries over into other kinds of physical comedy. Plus, it may have to do with the comic potential of the incongruous: it's funnier to see a big, burly guy giggling his head off than to see a petite girl doing the same, all potentially erotic elements aside.
Over all, I imagine women get tickled more often than men do, because of the whole size and strength thing, and because, perhaps unfortunately, it's a way for guys to touch girls with whom they're friendly without being overtly sexual.