From how slowly WoW "evolves", they don't need to cancel anything in order to continue it's development. And besides, there are MILLIONS playing WoW non-stop, that must mean they're totally into what's already there.
Blizzard should think about their other fans as well, I'm personally not a WoW hater, just not into that sort of thing, but there have been absolutely no games in the SC universe apart SC and SC2 which are like 12 years apart ...
SC being my all time favorite RTS

.
Edit: But hey, at least the SC2 single player didn't disappoint, haven't tried BNet yet but it sucks hard that they removed all possibility of LAN ... the cash-hungry whores. (They only did it to get more cash out of the Korean televised matches, because the "pirates" will eventually find a way to emulate the new BNet just as they did with the first, so it's just an inconvenience for them)