Nope. All of the National HD channels that were around before this new rollout are in MPEG2 and will be that way for some period of time (no one knows exactly how long, or they aren't saying). Only the HD Locals, and the new HD channels are in MPEG4.
They are in the HD pack because they don't have SD counterparts - that part is right - but it has nothing to do with MPEG2 vs. MPEG4.