RoVi (provider of the channel guide data for comcast and many others) bought TiVo for the remaining patents TiVo owns and have not expired. Several articles on the web have pointed out that RoVi is not interested in selling hardware at all preferring to sell the guide info to other parties. TiVo hardware itself is probably at end of life development with the 4 tuner Bolt that requires a cable card.
Comcast's future is migrating to IP delivery as opposed to cablecard QAM delivered content for TV.