ok - perhaps reading too much between the lines here, but I've been thinking about it a little.
Tim Cook gets a mail from someone (can't remember exact details so I'll paraphrase) saying "what about your professional community, you don't update the iMac and the Pro 'upgrade' was disappointing." Tim comes back quickly with a reply along the lines of "au contraire, we love, love, love our professional chums and we have something awesome coming for you late next year."
This sparks a number of reactions and a hurried message from another Apple spokesperson to say that Tim was only referring to the MacPro when he talked about 2013.
So, this says to me, Tim knows there's something awesome coming in the next 12-18 months and while he was not specific about the model, he was more specific about the audience. Whatever is coming between now and then will not be as good, because Tim didn't think to say something more positive about the rest of this year.
I can imagine spokesperson saying to Tim, "everyone thinks that nothing's happening to iMac and MacPro until 2013 because you said so. What about that speed bump to the iMac" and Tim replying, "Yeah, you can't count that as an upgrade really. It's more like what we did for the Pro."
So, my considered opinion. Bump this year, redesign and range revamp in 2013 - perhaps even an amalgamation of the Pro and IMac lines somehow.