By the way, watching The Walking Dead on this thing was pretty darned awesome.
Many ongoing tv shows look really good at 1080p (or 1080i) resolution, whether on bluray or hd broadcast.
Recently I finished watching the season 1 bluray set of "Person of Interest", which looked spectacular. Way better looking than the season 1 dvd version, which came with the bluray combo package. (The bluray combo pack had 10 discs: 4 blurays and 6 dvds).
During this past summer and early fall, I watched through four seasons of Fringe on bluray, and Hawaii Five-0 and Nikita reruns on hd broadcasts.
Kinda hard to go back to watching standard resolution 480p/480i stuff (such as dvd), after watching 1080p/1080i hd resolution for awhile.
Some older tv shows and movies take some effort to upgrade to 1080p, such as the original Star Trek and the Next Generation (or the older James Bond movies). They went back and scanned in the original film reels at a really high resolution, and redid the special effects. The season 1 bluray set of The Next Generation looks spectacular.
More generally, I doubt many studios are willing to put in a lot money and effort into such extensive restoration, if there's very little to no demand for such a product. Such demand would usually come from either bluray releases and/or off-network syndication of the show in hd. (The Star Trek reruns I watch every day, appear to be the same hd restored versions as on the blurays).
Though at this point, it appears that there's very little to no demand for older tv shows on bluray. For that matter, many popular and/or ongoing tv shows are not released on bluray at all (such as the Law & Order franchise, Criminal Minds, Two and a Half Men, NCIS, CSI: Miami, CSI: NY, etc ...)