It all depends on what operating system it runs in my opinion. Most tablet operating systems are just glorified, "user-friendly" cellphone-based systems (Android, iOS, WP7), and should not be on Super User in my opinion. If the tablet runs Linux/OSX/Windows 7 or 8/Unix, then it's fair game.
Why? Well, can you create and program an application while running the device? Do you have the flexibility and choice of compiling your own applications that run on other operating systems?
I'm not saying that you can't do these things, but use some common sense. There's so many applications I use on a daily basis that work on Windows/Linux/Mac. And if it didn't, I could (in most cases) easily just compile it on the new operating system.
The same can not be said for most phone/tablet operating systems, and I think that's where we should draw the line. These are highly embedded devices with very specific hardware and software requirements, removing most of the modularity from the system - and that's what a "computer" is all about.
If the operating system shares it's roots with a cell phone, then it should go on it's respective Stack Exchange website (i.e. Android.SE, Apple.SE).