There is a reason they are not releasing Tron on BlueRay -- the movie graphics were interesting in 1982, but they would look AWFUL in high def today. Remember, this was early CGI, and it looks pretty bad.
In fact, the movie has been discontinued even on regular DVD (which is why it is selling for 49 bucks a pop for used versions on eBay).
Second, the movie wasn't a success when it came out. Some people loved it, most hated it. People have fonder memories of it than the actual movie. Parts of it were never fully completed and are just drawn in rather than computer animated. It's glaring when you watch it. Bruce Boxleitner's acting is virtually unwatchable. The movie has no ending (at least one that makes sense in context of the movie). I saw the movie one night in Greenwich Village before class at NYU when I was in Grad School, and it was just so awful.
Third, the last thing they want is for people to see Tron before the "sequel" (read: "remake") with modern CGI is released. I'm looking forward to it, and from all trailers, it already looks fantastic compared to the original.