Honestly i don't think N8 sales has much to do with it. N9 will easily be 100 euros more expensive than the ~470 euros N8(price probably drops even more by the time of N9).
It's not like Nokia is in the position to delay it's top end flagship phone, just because one high end phone is selling great like they maybe could have done in 2007. They need all the people they can to jump to Qt or MeeGo ship. Android is gunning very hard currently.

Meego not ready sounds much more to be the real reason if we wont see N9 in MWC.
Unfortunately it's also something that the guy i talked about previously has said that things are moving very slowly on the MeeGo side and the UI had big revamp not too far ago(because of Skillman maybe?).