And even if one can generate traffic to the website (like a video store) how does the potential movie watcher know which movie to buy?
Thia is the central issue for any indie film-maker regardless of the distribution method.
The truth is that even with a regular distribution deal no film is ever going to pull real revenue unless it gets some kind of buzz going about it.
For my money I think that this is where viral advertising comes in. If you've got a strong enough concept for a film and you cut a wicked trailer, I think it's possible to generate an audience for that film simply by e-mailing the trailer to everyone you know and asking them to forward it to people they think would like the film. Even if you are "Johnny No Mates" you could do that within the indie film making community and within the cast and crew.
I think this would really separate the players from the wanabees, because virals only work if people like what they see enough to recomend it to their friends. It really comes down to the quality of your trailer and the strenght of your concept.
If you're then selling your film online you ask for the buyer's e-mail adresses; they then becomes the first e-mail out for the next viral movie trailer.
If you're setting up as a distributor rather than a filmmaker the best thing to do would be to profile your buyers with some screening questions (do you prefer horror, comedy, thrillers or etc. etc) Then you just do a monthly e-mail letter with hyperlinks to films they may be interested in.
I think the key here is understanding virals (which even the advertising industry is having trouble with) :
Selling a film via a virals means radically rethinking your approach to your trailer. Most of the best virals work because they are shockingly funny, or when people see them they are "blown away"; this means that just cuttting a regular trailer just isn't going to make this style of marketing work, because although it may persuade someone to look at your film, it probably won't be strong enough to make someone immediately forward it.
I saw a documentary recently on old indie exploitation film-makers from the 40's/50' and 60's. They were talking about how as film-makers they felt more like Carnies, in that they had to have some kind of outlandish hook to draw the punters in, much in the way a Barker would. I often think that although the new technology opens new doors, in terms of selling films is concerned we would do better looking at the past; I think a bit more PT Barum in our thinking would go along way.