Is that because of warranty concerns or because it just does not work. If not, why?
I believe some older DVRs (501, 508) did allow you to swap in a larger HDD, but I'm not positive now. I read about it over at Yahoo!'s Groups...
Why does Dish hard-code the partition information ?? Basically, because they can. Then again, apparently even the DVRs pre-522 were setup for VOD, that is, they have a reserved partition. In that case, Dish has a "boot" partition, "system" partition (OS and related files), "user" partition (where our recordings are stored), and the VOD partition. Now, one could argue "make the 'user' partition the last one on the drive and allow it to be as large as possible" and that's certainly a possibility. But, Dish chose otherwise.
As for the 522, 625, 622, etc, etc, you can buy them outright, but Dish's main intention with these was that they would be leased, not bought. If they're leased, they're not "ours" to tinker with.