This^Blizzard's claims about needing to protect their IP don't really hold water. It's not even clear exactly what IP the Nostalrius guys were violating. All of the actual content is contained in the client, the Nostalrius guys just reverse engineered the server code. They weren't using any Blizzard code or assets. Even if that were not the case, Blizzard granting these guys a license to their IP would not have been hard. Give the Nostalrius guys a perpetual not transferable license to run a WoW server, charge them $1, job done.
I also don't buy Blizzard's argument that it is too hard to set up a Vanilla server. A bunch of hobbyists literally reverse engineered a Vanilla server and got it running stable. How hard can it possibly be for professionals who actually have access to the original source code?
I can't believe they shut it down just to say it would be too hard to do haha.