The MPEG-4 letter from Comcast

Hey gang-

Got a letter today from Comcast/Xfinity that our Tivo Series 3 (and I'm assuming they mean our Tivo HD) is not compatible with an upcoming change to their service (MPEG-4).

Surprised to not see this here or in a sticky or in the Official Comcast Cablecard thread. (Yes I searched so everyone just be nice.)

Is our trusty Tivo HD really hosed?

Thanks!

Kupe