We've been able to verify this auction's authenticity through an anonymous source. We are certain all of the signatures are from the World of Warcraft team at Blizzard. However, this is not an official Blizzard auction -- but just something that everyone participated in as a nice thing to do.
This is the kind of collectible anyone reading this site would probably want. I know the WoW.com team began bidding furiously when we learned of its legitimacy. I imagine many of you will as well. When we learned of the poster the top bid was at $42, however now it's up to $100. Something tells me it won't stay there for long.
Update: We want to note the person running the auction has updated their post to say that this is a print of the original item.