I think it's the smarter move from AMD to release a 12 core imho. Just enough for what feels like an upgrade worth the 66% increase in price, but not enough to make people who buy your more mainstream $329 product think they are getting shafted. As much as power users feel like we matter to the bottom line, it's the $200 spenders that make companies money. If AMD immediately release a 16 core chip, it basically would tell their $329 users they are the new "Average". Could bite them in the butt.
Yeah, it makes sense to leave the 12c as the highest end for now. Having the best is very important in these markets and if AMD's promises hold true the 12c R9 is going to be a monster at $500 and get AMD all the media and consumer attention. Then they'll have that 16c in their back pocket that they can use to get even more attention down the road.