Except things aren't so good. If I rip a DVD, I can watch the resulting file on any computer in the house, running any software I feel like. I also have the opportunity to remove all the ads, previews, and warnings. On top of that, if I'm feeling flush on hard drive space, I can keep the full DVD (or even BluRay) size and quality. On the small number of downloadable movies today, I don't have these benefits - there may not always be previews, but the quality is typically well below that of a DVD and I'm limited to using the software linked to the download service. That's not convenience, and it's not better than ripping a DVD. It's worse, in nearly every way - and on top of that, I'd still pay the same for the movie, even though distribution costs are lower.
If some studio would allow me to download a movie for less than the cost of a physical disk, without all the previews and ads, in a high-quality format playable on any platform I like, the number of movies I buy would go through the roof. I'd even pay more for a high-definition copy - I'm still on DVDs because I don't want to shell out for a BluRay drive or player, not because I'm unwilling to pay a bit more for quality in the movies themselves.