BR
I think it depends on the show. Generally people like a bit of nostalgia and anniversaries can give shows the chance to break from their usual routine.
I find it hard to believe that the average viewer actually gives a stuff about TV shows' anniversaries. I can't help thinking on these occasions they should bring in a cake for the staff, and spare the viewers the self-congratulatory navel-gazing.
I think it depends on the show. Generally people like a bit of nostalgia and anniversaries can give shows the chance to break from their usual routine.