There have been attempts to "fix" this problem, but they have all been half-baked and as far as I can tell, intentionally neglected (or even sabotaged) by the cable companies. The latest, tru2way, promised that you could use any TV/DVR/etc for interactive features (CableCard is one way, no On Demand -- and even CableCard, although it works for some, is a mess in terms of billing, etc). Of course, only one TV by Panasonic ever supported tru2way, and it has been discontinued. No DVR's were ever commercially available.
This is not a difficult technical problem. This is a game being played between the FCC and cable companies. The FCC mandates that cable companies open up, the cable companies come up with something that looks good on paper, and the whole thing goes down in flames because the cable companies have no incentive to follow through. Cable companies don't want to give up the revenue generated by forcing customers to rent absolute crap set-top boxes and DVR's. And the FCC just can figure out why this isn't working...