PVRs don't always have the same feature set as what Tivo offers.
Questions that you should ask about any non-Tivo DVR
1. Does it have the ability to record all 'first run broadcasts' of any show on a specific channel? That is, it'll record all the new episodes of Joey on NBC, no matter when they air, but skips the repeats.
2. Does it offer the ability to jump forward and backward easily?
3. Does it offer HD recording capability (DirecTV w/integrated Tivo)
4. Does it offer to record all shows on a specific channel no matter when they are aired?
5. Does it offer one touch recording?
6. Does it maintain full subtitle and show information on recordings?
7. Will it automatically compensate for shows that are '2-hour specials'?
My cable box w/DVR built in does all that and in my opinion is functionally equivalent to Tivo. But, I am sure a few things are still not quite there and it is cable company provided, so they have a lot of control over making it work correctly.