...and it's for a simple reason.
There are two iOS devices in our household - my iPod Touch, and the "family" iPad. The iPod has "my stuff" -- music and apps that only interest me. The latter is more geared towards the kids -- children's videos, songs, and games.
I maintain a separate iTunes library for each device, though both are tied to the same Apple ID, so that I can purchase content once, and load it onto each device as I see fit.
Apple's cloud service, however, forces me into two undesirable options:
1) Getting to buy everything once, but forcing me to keep copies of all content on all devices.
2) Setting up multiple Apple IDs, and having to buy multiple copies of anything I want to have on more than one device.
Neither of these appeal to me, so I have no interest in giving up PC-based syncing.
Keep trying, Apple...