I hope they add that at some point.
I hope they don't. One of the drivers of putting multiple users onto one "Personal Computer" is because it isn't actually a personal ( as in one user) computer. That is in driven by the fact they PCs cost more than more personal items. Once everyone has one ( and not the price point is not there yet. ) that aspect will drop out. I hope they drive the cost down so it becomes largely a non issue.
Likewise if there was ubiquitous internet and infnite bandwidth your stuff could float out in some server and this would be just a viewer (you'd log into the server more so than the individual device. )
The other thing that is really starting to look antiquated is locking each device to a desktop machine and iTunes syncing.
iTunes Syncing (for those with relatively modest storage requirements) is really iTunes "back up". It is more like TimeMachine/TimeCapsule that the desktop machine is adding rather than syncing.
It is still quite necessary for people who have a bizillion photos , lossless audio, huge DVD collection , etc. that is much more economically stored on hard disks than on Flash. Hard Disks will stay the lowest $/GB champ for many years to come. As most people packrat away every larger volumes of stuff each year, flash storage isn't going to catch up.
I think there's a market for the iPad for people who don't have computers, and don't want to deal with them
The problem overlooking is that it is rather nice for Apple in a service/support position if they can flush your iPhone/touch/iPad contents or even give you a refurb knowing that you have a backup at home. Just plug new (or 'mindwiped' ) one back in and you get your data back.
However, yeah.... in that the majority of Mac OS X owners don't have backups. ( or very bad backups ). It wouldn't be much different.
But right now you can't really just have an iPad, you also need to buy and maintain a desktop PC that's at least as expensive as the iPad.
We'll see. If it is really just "back up" process needed, then some software may show up later that allows back-up to remote disk. It will also be a bit awkward if Apple doesn't directly support registering the device from itself.
There is nothing technically necessary why you need one. Mostly just some legacy mechanisms that need updating and a few new, straight forward applications.