I tend to rewatch my TV DVDs far more often than my movie ones. With a film, you only get two hours or so to tell a story. Good TV allows you years to work through an arc.
I watch Dr Who, Firefly, Red Dwarf, Buffy, Angel, and Star Trek DVDs often. I tend to watch the Whedon ones more often than the Treks (sacreligiously, on this site, maybe) because they seem to be more arc-based, with things you didn't notice the last time around.