Jon Johansen Breaks iTunes DRM Yet Again
You're on the right track here, but the logical extension is that the DRM is unnecessary - what keeps people buying is the better and more consistent experience of buying from a place like the iTMS (and perhaps a mild warm fuzzy of doing things the legal way, and/or paying the companies and people involved). It's not the stick of DRM, but the carrot of a well-designed service.
As you say, the ability to conveniently obtain the music you want has driven your MP3 download count to nothing. Removing the DRM from the bought tracks would only strengthen that impulse, as well as extend it to people like me who won't buy unless there is no DRM (though I also won't be buying until the price is at least halved - the current rate remains exorbitant, even compared to CD prices where I live, and downloading shared music is legal here).