MPEG4 offers greater compression than the current MPEG2 programming. DTV has both MPEG2 and MPEG4 HD programming, but all new HD programming with be MPEG4 encoded.
The new D10 satellite went live yesterday and is primarily a MPEG4 HD satellite (they added 21 channels yesterday). The soon to be launced D11 satellite will follow suit.
The existing MPEG2 HD programming will be transitioned to MPEG4 over the next year or so.
DTV promisies to have 100 HD channels (mostly MPEG4 encoded) by the end of the year.
The UTV unit is not capable of decoding HD or MPEG4 programming.
Hope this helps.