For the best writeup on the story I've seen, head over to the newly created Livejournal community (here's their manifesto). If you agree with the plight of players who want emaciated magic addicts, feel free to sign the petition and become a Member of the Skinny Blood Elves Society (clocking in at 82 signatures at the time of posting). And dreamt over on LJ has an update on the subject, including rumors (unfounded, but still) that the bulking up of the Blood Elves won't stop at the pixels-- Blizzard might change the Napoleon dance, the twirly jump, even the voice acting. I think those rumors are unfounded at best, but this is beta, so everything's up in the air at the moment.
Neth has given us a blue post on the subject as well, and she says (not surprisingly) that Blizzard's only goal is to make sure the models fit in the world they've designed. However, right before that, she does say that the change was made "in response to concerns that the Blood Elf male appeared to be too feminine." So the devs gave them "a more substantial, masculine feel" to give "the impression of strength and a menacing presence." Draw your own gender-based conclusions about that-- I'm not quite sure "substance" necessarily means "masculinity," but apparently Blizzard thinks so.
And Ephraim, the player who original brought the change to the forums, has posted comparisons to other races (including the one above) that make the change look not as pronounced as it originally was. There's no question that players don't want gorilla-shaped Blood Elves-- it doesn't fit what we've been told about the race or the lore behind it (not to mention that, Pally excluded, the Blood Elves' lore sends them towards the less melee-inclined races anyway). But the question that remains is what Blizzard will do with that information. We'll keep you updated on any changes we see coming out of the beta-- hopefully by the time it hits shelves, Blizz and the players will have found a BE shape that they can both agree on.