personally, i think the huge number of job openings is spurred by the successful completion of WoW. the servers are having problems and they need many new workers to help maintain the game. they are probably in the process of creating an expansion that rebalances WoW and not making SC2. BTW, the job opening, as stated below, is looking to fill the shoes of the old diablo team, not make sc2. here is the job they want filled now.
Job Update 2/3/05
New Job Opening - Lead Game Designer
Blizzard North is looking for an experienced Game Designer to lead the team that created Diablo and Diablo II. If you've led the design of a quality shipped title and feel you have the talent and determination for the job, see the Lead Game Designer position for more information.