I'm in it for the special features because I want to know more about my favourite movies (it's a treat to watch 30-40 minutes worth of deleted scenes!). And I like the fact that (not withstanding DVD rot or what-have-you) DVDs will last longer than I will. And it's fun skipping to your favourite scenes without the hassle of rewinding, forwarding, then rewinding, then forwarding, ad inf. And also, they're portable, easy to store and clean, has subtitle options, I could go on...
By the way, like some people here, I don't "collect" DVDs per se. I buy only DVDs of my favourite movies, ones I know won't tire of after the 1,000th viewing.