If they had one planned, they pretty much had to. If they didn't, then they can't really skip it to begin with. It's quite amusing that you think they could possibly not have worked on it if they had it planned in the first place. Blizzard measures development in months and years, not weeks.
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You expect them to work on WoW in their free time? Otherwise, what's your evidence for your "so wrong" claim?
Besides, seeing what the competition is doing is a perfectly valid move. Not everybody likes doing the same thing at work and off the job, either.