No one can!
I didn't say any codec was better than another. All I mean is that DirecTV cannot make the MPEG2 they receive from the broadcaster any better no matter what they do to it.
It can only go down from there.
The quality of the MPEG4 equipment will/does determine how much worse the re-encoded MPEG4 or MPEGWHATEVER will be - if any. But it won't be better than the original!
...you're behind the times. Many networks are using MPEG-4 for distribution and have been for awhile.