As if there was any doubt, Nethaera has posted that Blizzard considers the sharing of any Wrath of the Lich King alpha information "extremely offensive and inappropriate," though it's a good question as to whom that is, other than Blizzard themselves. Here at WoW Insider, our policy is not to rehost or quote any leaked alpha information, though as a service to our readers, we've been linking to other sites where it may be found. But is it within Blizzard's rights to lash out at anyone who does host or discuss leaked alpha information?
As copyright holders, they certainly have ownership of any notes, updates, or models released, so it could be considered a violation of copyright law to rehost the information. But to really get to the center of the problems behind this leak, you have to realize where it likely came from: the Friends and Family Alpha release. A little while ago, Blizzard distributed the client for Wrath to a number of their "friends and family" -- probably a group that consisted of employees and their WoW-playing relatives, as well as likely some folks at Vivendi and Activision, other Blizzard partners like Upper Deck and Figureprints, and probably a number of high-end raiding guilds who've done a lot of pre-beta testing for Blizzard before. Somewhere in there was someone not quite as trustworthy as Blizzard thought (odds are that Blizzard at the very least collected a signed non-disclosure agreement from everyone that they sent the client to), and that person uploaded or otherwise shared the client, against the agreement.
Cut to a few days later, after that person shares it with another person, who shares it with one more person, who then uploads it to a popular bittorrent filesharing site, and suddenly everyone's got access to everything in the Wrath client, and even if they can't play it, they can still datamine and grab information.