Very simple you stated that users don't like the iPhone OS.
Well some people do not but a huge numbers of people do and it has changed the mobile phone market.
I can tell you that a lot more people don't like WinMO than iPhoneOS. Frankly a lot more WinMo users hate WinMo. Most are stuck because of some app they must have and are hopping that WinMO7 doesn't suck.
Taskmanager? I have not needed on on my iPod Touch. Now on my Android phone I do. I will not get an iPhone because of AT&T. But a phone shouldn't need a task manager.
The Cut and past is now and yes it dumb to leave it out.
All you other complaints have nothing to do with the OS.
No keyboard, removable battery, or camera are or where all hardware choices.
They do have a camera and a real GPS now BTW.
Not being able to install whatever you want is more a cultural issue. Apple offers a walled garden of apps. You have one place to look for them and only one place you have to market if your a developer.
It is a choice that frankly really seems to have worked well for the users and the developers for the most part.
But again that has nothing to do with the OS.
Just about the only problem I have with the iPhone OS is the lack of multitasking. Which I do find really frustrating.
The Palm OS does a great card with multitasking the the UI is every bit as good as the iPhone OS.
WinMo reminds me of Linux back before Gnome and KDE. Yes it works and you can do anything you want with it but it is just an ugly mess. The difference is that Linux was more stable.