I think you may be begging the question* by expecting a Great Divide, with mobiles on one side and non-mobiles on the other.
Concrete example: In CSS you can make @media rules for "screen" and "handheld". iPad follows the rules for "screen". (I detoured here to re-check. Also established that my iPad considers itself to be 980px wide.)
If you're thinking about display, an iPad is a screen (plenty of real estate, high resolution, reasonable bandwidth). If you're thinking about user interface, an iPad is a mobile (only one type of "mouse" event recognized).
* Assuming for the sake of discussion that everyone reading this knows what "beg the question" means. Hint: It does NOT mean "forcibly raise the question".
Check the user agent, other than that it depends on the perspective of the companies.
Per example, Android phones VS Android tablets differ "usually" because phones include MOBILE on their user agent while tablets won't. I say usually because as there are attempts to standardize this, some manufacturers just use phone apps and software to build their cheap devices.