Fuzzy '70's sports video

I noticed that a lot of old videos from the 1970’s, i.e. Bucky Dent’s thrilling home run (which is such a good memory for almost everyone), seem to be getting fuzzier over the years in such a way as to make the players look progressively less distinct while at the same time giving them an almost furry halo — which makes for a rather nice visual representation of memory itself among bad nostalgic sportswriters. Cecil wrote about the issue of CD degeneration, but I’m wondering exactly what is the shelf life of video tape. And are we in danger of losing stuff we might want to keep the same way a lot of classic silent movies were lost or has this problem been solved by transferring everything we can get our hands on onto DVD?