Quite true. I'm excited that an OS that works well with my computer will be availble come June.
Yes, form factor and features, SOME of which come from 3rd party apps.
I don't know if you can argue with the form factor of the iPhone. It's thin and sleek with revolutionary touch-screen technology. Sure, many complain about the non-tactile keyboard, but how can you knock it till you've tried it.
As far as the 3rd party apps that compel me to be a Treo user...
I won't need pTunes anymore as I'll have iTunes...
I won't need 3rd party browsers that may or may not work, I'll have Safari
...
I won't need Missing Sync to sync data...
I won't need Missing Sync to have a "good" Memo app...
I won't need Agendus to get all my appointments and tasks to work with iCal...
I won't need Chatter to get my email...
I won't need FileZ to move files to make my phone work...
I won't need GoogleMaps because it will have it already...
I won't need Hi-Launcher because I can quickly tap on the screen and get what I need.
I won't need PowerRun because I'll have 8 Gigs of space on the HD...
I won't need SplashPhoto because I'll have the Photos application...
I won't need TCPMP because I'll watch videos under the iPod app.
I won't need Volume Care because the Phone app should actually work(out of the box)...
I won't need TreoGuard because the screen has that technology built in...
The only thing I really am concerned with is my SplashID app to store passwords. I hope there's an app or a widget for that.