In either case, even though it isn't possible, you'd have to spend money on a sat tuner card or a receiver, so it works out the same. There isn't a huge market for this and the support cost would be huge, so not likely to become available any time soon.
The way you posed your original question "watch on computer" is of course possible as described above. I feed composite video and L/R audio into an old analogue TV tuner card from a 5900 Bell PVR and occasionally watch TV via my 24" LCD monitor. I maninly use it though to grab a few screen captures here and there.
A satellite tuner card woiuld require specific hardware to the vendor so 3rd party stuff would be unlikely. It would also have to deal with frequent firmware updates and handle a smart card some how. The other drawback/difficulty would be that your computer would have to be on most of the time to maintain authorization.