I've always thought it was strange that so many people who bought VHS tapes rarely watched them. And then a lot of them bought them again on DVD! They needed to own Sex in the City, The Godfather, or the Star Wars trilogy, but never even broke the seal. Maybe they buy them as keepsakes, to remind them how much they loved the film or TV show, but don't actually need to see it. Or they watch it once and that's all they need. Big multi-disc box sets can be daunting, I bet half the ones sold remain unviewed.
Sure, it looks like downloads are the future, but how does that jive with the desire to covet your favorite films? Millions of people keep buying new editions, Director's Cuts, 20th anniversary editions, remastered Sopranos, and some smaller number will buy them again on Blu-ray. Will the keep buying new downloads of old faves?
Maybe it's just that people crave a physical connection to the things they love and virtual facsimiles don't cut it. Physical media may be impossible to replace--its actual usefulness doesn't seem to be the point.