Yeah, but think about the potential: a TeraTivo where a certain percentage of disk space is reserved merely for recording all programming on all channels for a certain number of days in the past.
Let's say you come in to work one day, and there's all this talk around the water cooler about this amazing, unexpected thing that was on TV last night. With that kind of storage, you could have that at your fingertips when you got home.
Or the simple "D'oh! I Forgot to set the Tivo to record that!" problem would be solved.
Of course, nowadays, both problems are solved when you've got the ability to share and search with all other PVRs on the internet... I wish that were a universal feature.