This obviously isn't the _only_ type of artist on SoundCloud, but they're a huge part of what makes SoundCloud culturally significant.
DJs are in the derivative work business, no matter how much they claim to be innovative or 'making something new!' by mixing tracks together, and while I'm an advocate for Copyright Reform, for now the way laws and commercial rules are written, DJs making and uploading mixes don't have a leg to stand on in the SoundCloud model.
It really does seem to be the proper platform for DJ mixes.
> Mixcloud streams the mixes and radio shows of its registered users and pays performance royalties by way of its agreements with licensing collectives around the world.
http://www.billboard.com/articles/business/6221953/mixcloud-...
That's why MixCloud is for mixes and SoundCloud is for individual creators (or their PR machines who effectively control the rights to the material).
As an Ableton Live and Propellerhead Figure user, I've always been amused by the "Upload directly to SoundCloud!" plug-ins / capabilities, because on the one hand "Yay, convenient!" and the other hand "Wait, I've still got to master these and bounce them to mp3s for other uses."
The simple truth of reality is that a lot of music is only available through soundcloud.
Smart? No. But it's how things really are.
To put it another way, SoundCloud at its core is a free streaming site, and it also allows free downloads if enabled by the music act. There is no way I know of to set up SoundCloud for paid downloads or streams. Thus, using Bandcamp, Spotify, iTunes, Amazon, Tidal, Google, Deezr (etc) are wise to capture a modest revenue stream and listener data in ways SoundCloud simply doesn't support.
SoundCloud a lot more like Facebook than it is iTunes: socially important, great for sharing, a way for something to go viral - all important angles in modern business, sure. Is it such a monolith that I'm worried about its future? Not really; it'd be sad to watch it crumble (further, in some respects) but that doesn't seem likely for at least a couple more years. Lots can change.