The idea is that the independent DJ will pay any amount to get a 320k quality version of new song to play at parties and local clubs.
I've bought $1.50 tracks from Beatport before and the quality is top notch, but anything more than that I wait to buy on AmazonMP3 for a dollar.
What's interesting is that other online dance music stores charge that $2 and up per track price too. It's because the catalog these stores offer is largely unavailable on iTunes, AmazonMP3, Zune Marketplace, Spotify, etc. So you can't get it anywhere else unless you pirate it, and even then some of these tracks are hard to find. Trying to find a download of a full, unmixed dance music track can be tough. Most of the time torrents have these tracks, but they're not full versions (they're ripped out of someone's podcast or radio show, complete with watermarks).