Do we really need three different tags for different models of the same device? iPad 3 - no memory warning?
Yes, they're just bits and they don't take up much room, but isn't this what tag synonyms were made for?
There is such a great difference in hardware between iterations of these devices (the third-generation iPad has a Retina display, dammit) that it would only be sane to have tags for questions that pertain only to each of these models, given potential compatibility issues with apps and such. We do have version tags for all kinds of software anyway, so I don't see any harm in having "version" tags for the hardware/devices that we build software on.
I have no comments about ipad-3; I think we can just leave it at that since the third-generation iPad doesn't have a distinguishing name from the first-generation one, and "iPad 3" has been a popular nickname for it.