yeah, what did you think a game's development cycle looked like?  I mean that would only be a couple of years in the works for elemental.  not everybody that worked on creating the base game of GC2 would have to be working on twilight.   So they would be working on the next project.

Blizzard's been working on starcraft 2 since warcraft 3 came out.   And when elemental comes out there is likely going to be plans for whatever comes next.   otherwise people would be paid to do nothing.