The biggest reason that Tivo hasn't grown is that they don't control the content delivery system. The cable industry has fought hard to keep from standardizing on things like CableCard because it would mean they no longer have a monopoly on the delivery hardware for their own network. With a delivery standard you could purchase a Tivo box that would work with all cable providers without the need for an IR blaster or other hacks. Apple had iTunes in place to deliver content. Tivo clearly was innovative and wins in the UX department but the cable companies have done everything possible to ensure it doesn't succeed.