The frustration is not that it's different or less, it's that it could be better if apple was actually willing to try.
You don't need to sacrifice composability just because of the tablet form factor. You need to be careful with the input methods, sure, but composability on a tablet could actually be better than on a PC if designed well, but we'll never know until someone bothers to try.
I'm in the camp that thinks Apple made a mistake adding multitasking to the iPad. I don't want my iPad to be more PC-like. The changes were significant and iOS is less stable now than it used to be. Even if they get all the bugs ironed out, I'm still a little sad that they clearly want to take the device in that direction.
For similar reasons I thought Microsoft made a big mistake dumping the Windows 7 UI for Metro (or whatever it's actually called).
If I want to do PC-type stuff, I'll do it on my PC. Tablet stuff I'll do on a tablet.
I don't really like the multitasking implementation, and I definitely don't need it. Multitasking was never one of the things standing in the way of my iPad being a PC replacement for me.
You don't need to sacrifice composability just because of the tablet form factor. You need to be careful with the input methods, sure, but composability on a tablet could actually be better than on a PC if designed well, but we'll never know until someone bothers to try.