I can think of a few other advantages and uses:
Lack of maintenance: No complicated configurations, no virus scanners, no trouble shooting (well, for the most part), etc. Apple and other manufactures have a simple model to solve problems: you go and buy a new device. Backup is handled by whatever computer you use to sync your device with so transitioning from one device to another is relatively easy.
Quick access: People leave their tablets in the living room, kitchen, etc. so whenever they need to search something online, check prices, play a game, follow a recipe, etc. it's right there in front of them. Sure laptops can do that too, but laptops are still mostly associated with "work" and or often too expensive and big to just leave around for someone to knock over, etc.
Not as valuable: You have your important stuff on your desktop or laptop, people treat tablets more for casual stuff and are less likely to store important content on them. And because you can sync, there's an automatic backup (well at least with iPads, I'm not sure about other devices). So there's less fear associated with a tablet breaking or being lost.
Application Store: The general public is used to making purchases at stores. Buying something on a tablet is easy (for the most part), you don't have to visit different websites, all with different registration and purchase systems. Instead, you remember a single username and password and you are good to go. Updates are handled through the same system as well.
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I'd say that for the general public, a tablet can do almost everything they need and they are a great way for someone to get into computers without much hassle (speaking from my own experience with my mom).
I'm sure that many people buy tablets for the novelty/status/games/whatever, but I think they have a lot value for "pro" users as well. For example, you can use them as controllers for audio and video applications instead of buying expensive physical hardware. Photographers use them now as portable portfolios. Event organizers use them instead of a stack of papers for keeping track of schedules. Etc.