Hmm. I just reread my early post about the Rolling Stone 50 list and realized it appears to have been edited by a chipmunk (moi), who while cutting large chunks of rambling also decimated the point I thought I was making.
It's not that Rhapsody doesn't have a good selection. It does. Most online services have similar content, because once the music labels finally chucked their Napster-terror and agreed to online distribution, they OK'd it for everyone. (Credit my old alma mater MusicNet for contributing a lot of the groundwork.)
So when an artist's entire or near-entire collection is inaccessible, it means that whoever owns the rights just isn't interested in online distribution. And when you see a list of about 40 top artists and only a handful are still balking, well, I think a little exasperation is understandable.