I've heard about the Comcast Tivo, but it's never been advertised in their product/pricing guide filed with the local franchise authority so I'm not sure that it is even available in my area. Regardless, Tivo placed an Xfinity On Deman app on the Tivo Premiere and my parents and I love it - works great! That was the only disadvantage of having the Tivo. FiOS is being installed in our neighborhood in VA, but I just renewed for 3rd straight year under a Comcast promotion ($119 for all their digital channels to include HBO, SHO, MAX, Starz, etc. and the Sports Package (BTN, NHL Net, MLB Net, NFL Redzone, etc - plus 30/15 Internet) and the FiOS promotion is more expensive, offers less, and I'll lose the Xfinition On Demand app. While Comcast may not install many Cable owned Tivos, I love how they're supporting customer owned devices.
What I meant were "private" agreements. The Comcast one is very different - TiVo designed the entire interface (and boxes ?) for them. Supposedly Time Warner or possibly Pioneer, who developed the Passport software used on TW boxes years ago, had licensing agreements either providing them the software or at least a "we won't sue you" license.