Sexual Dimorphism
From the department of saving the world one pixel at a time, we have a nifty essay on body types in World of Warcraft. I don't wholly agree with all of the conclusions--for one thing, Tauren, dwarf and gnome women especially are not precisely what I'd call "in line with traditional Western beauty ideals"--but it's an interesting look at the overall trends. There are a couple of outright errors, too--troll women can have tusks large enough to be visible in screenshots, and Tauren women do have horns (you can even select the horn style, and the fact that they're smaller than men's horns is entirely in keeping with the cattle the race is supposed to resemble). For that matter, Tauren women are taller than the men of most other races; I think the only exception is the draenei.
I do wish WoW offered more in the way of character customization; it doesn't make a huge amount of sense that a bookish mage or priest would have the ultra-athletic body that is the only option, and as someone who's well-endowed in real life I don't feel a great need to have a pneumatic1 avatar if that's OK.
And I find it interesting that the author doesn't point out (that I saw) that the blood elves were designed specifically so the Horde would have a "pretty" race. For a long time, you had to play a female troll if you wanted a Hordie who stood up straight (and now your options are "female troll, or blood elf of either sex"), and few of the face options for the original four Horde races are terribly attractive by conventional standards (the troll women are again an exception here, and there are one or two Forsaken faces that aren't too terribly rotted). Even Alliance-side, the gnomes are decidedly cute rather than pretty, and the lack of dwarf women is something of a joke; unlike in LotR Online, you can play a dwarf woman, it's just that most people don't2. And the rare dwarf female is a solidly-built person indeed; she's not willowy, slender or slim by any stretch.
As for the difference between builds...eh. WoW's overall design is very cartoony (which means it'll run on most machines, which is nice), and that style lends itself to exaggeration. The draenei are extreme, yes, but I can see how they're part of the same species and that's enough for me. Plus, I love my all-white draenei shaman and want to get her to a high enough level that she can wear [White Wedding Dress], because it'll just look cool.
1: Vaugly amusing note: Blood elves and night elves (and possibly trolls, but I've never played a male one and females have shorter ears) have long ears that wibble when they run. No one's breasts, however, are anything other than rock-solid no matter what the character's doing.
2: Unless you're me or my friends, apparently, because there were five I know of at last count (though Breska was decommissioned the last-time-but-two Shawn quit the game).