I don't customarily respond to these threads as it's pretty hard to sway any one's opinion especially when the first thing they say is "Yes, this is pretty much a rant." Nothing I say here is 'official' by any stretch but I feel like I might be able to shine a little bit of light on some of your points.
A simple, tidy, non-flashbased website design.
However clunky, working with certain platforms allows for more seamless integration of things that you would come to expect from a music store (ie persistent playback while navigating between pages without popups etc). Flash was also able to ensure that all people who could load the site we're having a similar experience dispite having different operating systems, browsers, etc. Luckily web standards are getting to the point where this is becoming less and less of an issue. At the end of the day we're really just looking to provide the best discovery experience and aren't really married to any platform in particular.
A good search function
Ahh search. What would you type into the search field to find a particular track? If you ask the next guy their response will probably be different. Do you want to be able to search by track name, remixer. producer, label, genre, sub genre, keywords, other songs that sound like this? Sorted by newest or most relevant? It's a lot more involved than most think.
A few months ago Beatport pushed out the "Beta New Search" which works much more like traditional internet searches. Some people love it, some people hate it, some people don't know the difference.
Full previews. Yeah, come on it's not like anybody will not buy a release because you can fully preview it. This is ridiculous and just show's the "fuck off" attitude of most stores.
This has to do with publishing rights, associated fees, and precedents set by the old music world of physical sales and broadcast and is really more confusing than anything else here. We know people aren't going to play out these lower quality samples (at least no one I'd want to see play) so people snagging the previews isn't really the issue here.
reasonable prices. Yeah. 1.50 to 1.70 euros is NOT reasonable for a fucking file. This is pretty much a "You gotta pay for piracy" attitude. A file format of your choice at the same price. Yeah WAV/FLAC maybe cost a bit more bandwidth, but did these stores ever hear about something like being "Customer friendly?". Hell yeah I love "supporting the artists" if they get 0.35 out of the 1.40 I paid
Music stores for DJs don't provide the same product as commercial sites. Most niche download site will agree that they're there to provide a valuable services that stretch far beyond providing a link to a file to be downloaded. We have an army of label managers and genre managers to comb the world looking for the next best sound. Sites introduce new artists and labels and constantly reinvest in our community. Can shops do it for cheaper? Possibly, but you probably wouldn't want to shop there. Also if the artist are only seeing .35 they'll want to make sure their label is collecting international sales royalties from ALCS/GEMA/etc.