They won't follow until they get new SATS up.
There are too many users with the MPEG2 decoder boxes (including me) to start moving things over to MPEG4. That would leave MPEG2 users w/o those channels.
They need to start giving free upgrades to the MPEG2 boxes...
I have a feeling, in a few years time, all channels will be in MPG4, HD & SD. One receiver like the H20, will be used for all customers. Most broadcasts will be in 16 x 9 HD and the receiver will downconvert the HD signal to SD, with black horizonal bars on the top and bottom of the screen, to accommodate the last of the 4 x 3 screens that are still being used.
Actually this could be done today, if everyone had H20 receivers and/or HR20 DVRs.
Think of all the bandwidth that would free up, putting everything in MPG4 format and eliminating the duplicated transmissions of stations like the ESPN's, HBO, Showtime, TNT, etc.
O well, just a pipe dream, with a lot of reality.