It sounds to me that Apple just didn't have enough time to finish all that they wanted to do. No doubt Steve wants everything to be Push.
But let's look for a second at how MobileMe on the desktop is currently working:
- The behavior in my mind is a lot like TimeMachine:
1) it's looking at all of those items on the list of checkboxes in MM prefs
2) Compares that to the server
3) works out changes
4) Uploads
there's quite a bit of overhead in those steps, especially when including Keychain, Dock, Dashboard, etc.
My guess is that for a complete Push solution, those transactions would need to be made at the Application level, similar to how Mail does IMAP, with each press of the delete key on a message it communicates with the server.
Similarly, for iCal, those server transactions would need to be built in to the application itself...Which I would imagine would take a fair amount of work.
Maybe I'm wrong, and I'm not justifying it. I would expect a Push to be less than 1 minute, not 15 like it currently is. But I also don't want my computer to be processing changes for ALL of those little checkboxes every 30 seconds or whatever.