What's sad is that there isn't a rich and vibrant world of companies making DVRs. On modern computers, you don't have to do anything special any more. You can decode and play HD video in software! I suspect the absence of good competition in the market is all about two things.

In the satellite world, the standards aren't open. You can't just build a compatible box.

In the cable / OTA world, where the standards are relatively open (at least to the extent that CableCard can be called an open standard), nobody wants to up against TiVo's patent portfolio. The patents in question don't expire until 2018. Maybe things get interesting then.