Here's the official word from Blizzard regarding the change:
As many players have noticed, we have made a slight change to the male Blood Elf character models. In response to concerns that the Blood Elf male appeared to be too feminine, and after reviewing the model from a visual and conceptual standpoint, the decision was made to increase the body mass to give them a more substantial, masculine feel. It was also important that as members of the Horde that the Blood Elves gave the impression of strength and a more menacing presence.Comparison pictures of the old and new models can be found at ActionTrip's article, along with some criticism of a change that may not necessarily make every player happy.
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