AVCHD's are in a format that can be burned to DVD-9 and played back on many Blu-ray players. They are significantly lower bitrate than the MKV's, and therefore aren't as good, although it should be noted that they're surprisingly good considering their bitrate.
EDIT: And yes, Harmy's still working on the 2.x series. Jedi is up next, then probably more work on Empire (it's not perfect yet).