Artist services are the opposite of a label
The key point is who’s in control.
A label owns the music and in a way, the musician. When an artist signs to a label, the label is in control.
(Too many horror stories of a label making Billy Squier wear a pink Flashdance suit and learn to dance for a video, or labels making their artists do a Christmas album.)
What I love about artist services is that the musician is in complete control.
The artist knows best. We’re just the tool.
I set up CD Baby just to help my musician friends doing whatever they needed help doing. The benefits of aggregation is that we can help them do things much cheaper and easier than doing it themselves, because we can build a system to do it for many people at once. (Negotiating distribution deals, sending files to iTunes, making artist websites, etc.)
As for arbiters of taste, I prefer the separation of duties :
Let editorial outlets like people’s blogs, WebJay playlists, or webradio (SomaFM) be the arbiters of taste, helping to call your attention to what they think is great.
Let the distributor be unbiased : getting all of their clients’ music to all outlets equally.
Then the promoters can be either paid up-front for their work, or agree to gamble and take a back-end reward, but not confusing paid-promotion with objective tastemakers, and not confusing promotion with distribution.