I'm not sure I see the sexism. Then again, I haven't played around with the character creator yet. If the widest waist you can put on a human female is still a few inches short of the girth of her rib cage, then yeah, I can see the argument.
In most of the examples people have posted, the women are definitely more idealized than realistic. But they don't seem to be overtly sexual (at least not the body models -- some of the armors are another story). They rather seem a little too beautiful to be real. Beautiful and sexy are not synonyms. In some cases they are almost opposites.
We can talk about the constraints ArenaNet have put on the character creator, and the ideals those constraints enforce. The most obvious ideals are "You can't make a grotesque characterization" and "You can't make a member of one race look too much like another." A less obvious ideal is "You can't make a character below a certain level of aesthetic appeal, because screenshots of your character represent our game." We can talk about whether that certain level of aesthetic appeal has been set too narrowly. We can talk about whether the doll faces with flawless skin that make up half the starting population of Kryta represent an unrealistic and harmful standard that young women feel compelled by society to measure up to. We can talk about whether the witting or unwitting propagation of this standard is inherently sexist, merely often sexist in practice, or not sexist at all. But I'm not ready to believe that ArenaNet designed the entire range of human female avatars primarily to enrich the sexual fantasies of pubescent boys, if that's what you're trying to argue.