The way X64 motherboards worked, and the way Ivy Bridge therefor works, is that an SSD is coupled to a second Hard Drive, but they appear as just the one drive. The SSD works like a cache for popular activity. So if you use photoshop a lot, then it will be move to the SSD, and hence will load quicker. The OS will also be on the SSD. I am not sure though, but I think that all the programs are also on the HD.
Its an Intel idea and very cool, as it greatly lowers the work a HD does, and an SSD being solid state is almost fault tolerant. it isn't, but they are dam reliable compared to HDs.
So ... I would be amazed if there was a single SSD only machine. I think logically, it will be a small SSD, and a hard drive, and they will appear as one single drive on the desktop. Just as Intel intended.
As far as the top iMac goes, I hope its an i7 ... and that there isn't another upgrade to a faster processor. With the current machines, you have to upgrade from i5 to i7, which costs a bit extra. the i7 is good for video and graphics.