said by castsucks :
TiVo does not get you VOD (you are paying for the free VOD) and some time events PPV.
Perhaps Comcast could argue that the VOD fee is built into the rental fee for the STB. You don't pay that fee if you replace the Comcast STB with a Tivo, therefore no VOD for you. I have no idea if that is the case, but makes sense, I think.