The only difference I can see is that the 4.1 has an inbuilt sim type card holder in it, which, along with a valid card, accesses a couple of extra mature content channels whilst enabling you to insert a standard card in the cam itself. As a Dragon will encode most stuff without a card anyhow, it does seem to be rather an expensive waste.
Most dealers supply the InXTC card (either sim size for the 4.1 or full size for 3.*) with the cam, so if you don't need a card for anything then go for the cheaper version.
Another point with this though, a Dragon can now emulate a well known UK systems hardware, provided it's given a box number. Therefore you would need an additional card slot if you want the pron as well.......
Hope this helps, though I think I've confused myself here!