Apple is holding a Mac-related event on August 7th. That is fact, not rumor. So wait at least until then. If there are no iMac updates announced, then buy since you really need a new machine. If new ones are announced, then buy a new one and hope that the shipping times won't be too terribly long!
As for WoW and SC2, WoW shouldn't be a problem. As for SC2, I doubt it would be either, but no one knows when SC2 will be released. Its system requirements will no doubt be releatively modest when it is released, but modest requirements now versus modest requirements 2 years from now are completely different matters i.e. the average video card a year from now is closer to a high-end card today. What I'm getting at is that SC2 could be released this Xmas or late 2008, we simply don't know yet.
All that being said, I should hope that the current offering is good enough for SC2 as I don't see it being a demanding system hog of a game, but we won't know until more details are released.