I'll come out and say that I agree with you... in theory. In theory, I wish I could pay a price and then be able to see my purchased movie anywhere. Real-world problems interfere with that ideal, however.
Movie studios won't just put the movie up somewhere where I could get it for free. They'll want to make sure that I'm actually authorized to watch the movie. This means they'll rely on DRM. This, in turn, means they're likely to rely on one location for authorizations to take place. If those authorization servers go offline, you lose access to the content you've paid for and need to pay again for access to it. In addition, movie studios aren't going to want to run servers letting you download a file over and over for one small payment. They'll want recurring payments.
This is why I think that streaming is the better option. Something along the lines of Netflix. Pay a fee and get access to the library of content. As long as you pay your monthly fee, you can watch as many movies/TV shows/whatever as your plan allows. (I'd prefer unlimited, but we are talking about movie studios here.) There should be many different companies doing this providing access to the same content. This way competition will keep prices low and quality high. (Besides, I'm sure the movie studios don't want Netflix to be to them what Apple/iTunes was to the music industry.)
Of course, I already have a Netflix account and love streaming via Roku, so I'm mostly there. Now if the movie studios would just get with the times and let their content be streamed. Heck, I'd even accept a 6 month lag on DVD release versus streaming release if they're that concerned with streaming cutting into DVD profits!