No real surprise.
It seems fairly obvious that there are two development paths for the iMac underway at Apple. There is a straightforward refresh which will involve Ivy Bridge CPUs, faster RAM, Kepler graphics etc - a straightforward refresh along the lines of the non-Retina Macbook Pro refreshes that were announced on Monday. And there is a new "retina" iMac in the works, too, which will be thinner, have no optical drive etc, plus of course a much higher resolution display. When Apple hints that they have something exciting in the world for iMac fans coming next year, this is what they are referring to. On the other hand, the straightforward refresh will be along in a month or two. Almost certainly, we will see a Mac mini refresh at the same time.
Apple never refreshes its laptops and desktops at the same time: it's presumably easier that way.