Well, Video sources (like GMA) tend to look sharper than film sources (like TWW) to begin with.
Then there's the production aesthetics, and TWW has never been one that tries to wow us with their HD picture quality. If you go back to a season 5 episode, Access, which was shot in HD video, and it definitely shows a tremendously sharp picture.
Do I wish they had a sharper picture on most episodes of TWW? Yep. But that is the production staffs call!
Cheers,