I gotta admit, I'm starting to shake my head and wonder how much sense it really makes for Apple to maintain this many versions of essentially the same product.
I mean, if they would have only designed the iPad so the back cover was possible to unsnap, they could have made custom memory upgrade modules and cellular upgrade modules for them.
Then you'd only have to sell a black and a white version of the iPad mini and regular size iPad. Buy one with 16GB and wi-fi only as the standard configuration and add your choice of upgrade modules if you want anything over and above that. Since they'd have to be custom boards, Apple could still charge enough mark-up on them so they'd make the same amount of money they make now on upgraded models -- but they wouldn't be stuck in situations where retail stores are out of models people desire, and have too much stock of ones that are selling too slowly for them.