Videos look awful in iTunes, much better in Quicktime Player

Question

I was, just as many others, deceived by the quality of video clips bought on iTMS (I started with the beautiful Love Profusion, by Madonna, and M.Jackson's Thriller).
The picture appeared in particular pixellated in sull screen, this for many videos.
(and the interface is so stupid : why do you have to play a clip in order to be able to switch to full screen, except maybe to keep Quicktime Pro's full screen in QT Player option alive ?)
Then I just remembered how my videos played beautifully in Quicktime Player, and often awfully in iTunes, since iTunes 4.9.
So I tried them in Quicktime Player (I have a 7.0 Pro license). (select in iTunes, command-R, command-O, command-F, you're done)
They look much much better.
And same goes for my non-iTMS videos, even after being converted to the iPod-friendly format with Quicktime Player.
I just remember reading from a member of the iTunes team how quick it had been to add video capabilities to iTunes (since 4.9 I think).
Maybe it was dine a bit too quickly.
I just thought it would have been fixed BEFORE the release of a video-capable iPod and the sale of video clips on the iTMS.
I now hope that on the video capable iPod (waiting for mine), these videos look more like in QT Player than like in iTunes Mac.
It looks like iTunes 6 forgets to or cannot do H.264 post-processing correctly. By the way, this post-processsing is part of the standard specification, according to Apple's technology brief
(http://images.apple.com/quicktime/pdf/H264TechnologyBrief.pdf), which means that the encoding process takes into account the de-pixellization done in post-processing (unlike divx for example, if I understand correctly), and that iTunes decoding is not even compliant to the H.264 standard.
Having such a bad, broken video player as iTunes 6 for both quality and ergonomy (at least on Mac) is SO STUPID.
I hope someone fixes the quality issue very quickly (Itunes 6.01?). If this person had time to make a "not as stupid as it is right now" interface for playing videos, that would make me happy again.
If anyone can confirm if this is a Mac only, or Mac WIndows issue, I'd be glad to know.

Answer 1

I do see a slight difference in quality between an .m4v file (purchased from the iTunes Music Store) when played in iTunes and QT player. If freezing at a specific frame, you can definitely notice the iTunes software seems to blur things and is less sharp (colors more dull, less pronounced).
As far as the interface is concerned for viewing videos inside of iTunes, the only real concern I have is the performance. QT player resize/scrubbing is much more effective.