This is one feature of Tivo that is really nice. Deleted shows are put into a separate folder, like the recycle bin on a PC, and can be "unerased." Of course, if the Tivo needs to record over that for space, then you will no longer be able to retrieve that deleted recording.
I suspect that it is difficult for Dish to do this without being accused of violation another Tivo patent. So, we may never see this feature with Dish. Still, overall, the Dish STB's are better than the Tivos