There was no Blizzcon 2006. There was never a guarantee of consecutive Blizzcons--folks just got used to it. They have enough stuff to actually get out the door as it is, so not having to deal with a convention only helps with the production schedule.[/b]
First of all, nobody buys that.
Second of all, BlizzCon 2011 took place while they were allegedly deep into the production of a bunch of games and it wasn't a problem. BlizzCon 2012 would be more or less a review on the production that took place in 2011. D3 should be out, and the MoP beta should be out.