It seems to me that squawk answered your question a couple of posts up. The answer is what I ofter call "standard answer #1 - It DEPENDS!" It depends on the quality of your set. It depends on whether the source is 720i or 1080i. It depends on how the source was originally recorded. It depends on the bit rate that D* feeds into a particular stream before the compression. And, as someone stated above, not every individual can discern the difference. My wife, for instance, cannot understand why I like HD so much better than SD. She can't see the difference. I don't think there is the kind of answer you are looking for.
PQ will always "depend." I use the acronym "STD" (Source-Transmission-Display) whenever I try to explain to someone general factors that impact HD video quality. Source is how the video content is originally captured & stored digitally. Transmission is how that digital content is transmitted from the storage medium to the studio to the sat uplink & ultimately broadcasted to one's STB & routed to one's TV. Display is how that digital content is converted back to analog on the display (i.e. 720p, 1080i, 1080p).
Relevant to this conversation is: (i) what DirecTV does with the digital source content is receives from HBO; (ii) does it use MPEG4 compression or MPEG2; (iii) to what extent does it down-res; (iv) to what extent does it compress the data?
(i) it's plain as day that video quality of a live broadcast (i.e. sports programming) is much better than a TV episode or film. IMHO, it has to do with how the original source is captured. Sports programming, because there's a lot of movement, requires source content to be as detailed as possible. Video info changes with each frame. Bottom line, HBO video quality is not the best to behold with an HDTV.
(ii) assuming HBOWHD is MPEG4, which a much more efficient compression scheme than MPEG2;
(iii) then given the elimination of "limited bandwidth," video is NOT down-rez'd.
(iv) so big issue, impacting PQ is to what extent is DirecTV compressing HBOWHD feed? If HBOHD under MPEG2 is compressed to, let's say, a 8 Mbps feed, in order for the MPEG4 feed to look better (notwithstanding the absence of down-res), the feed should be @ least 4 Mbps, more likely in the 5-6 Mbps range.
Bottom line to all this BS, is the pic quality we perceive with our eyes & our brain. That's the litmus test, not the above analysis. The analysis just explains it. Personally, its tough to compare the two HBO HD feeds unless you've recorded the same content off each of the channels 3 hours apart, & then compare. I haven't had the opportunity nor the desire to do that.
PS. My drive is close to full having recorded a bunch of films off the "new" STARZ HD channels, & non-compressed OTA feeds off PBS's "The War." Can't spare the extra drive space, plus always record MLB playoff games in case I miss.
PSS. Big positive for us HR20 owners is that MPEG4 recordings will consume less drive space than MPEG2 recordings, not to mention the much improved PQ (of some programming).