ArsTechnica has an article about Apple and the DRM conundrum. The suggestion is that Apple would never sell both DRMd and DRM free music side by side on the iTMS because of their commitment to a simple and uniform user experience.
While that may be their cover, I think that no one I have read has really stated the reason accurately: to differentiate between tracks that have DRM and those that don't, Apple would have to inform customers of DRM more conspicuously, and explain the difference between a track that has it, and one that doesn't.
The more Apple's iTMS customers fully understand what FairPlay is -- what DRM is -- the more unhappy those customers will be. So in a way, yes, it is because of Apple's concern over user experience, but not because showing a little icon, or disclaimer will confuse customers, it will upset them.