It sounds like some people are missing the point of these things, at least as I understand it.
I'm pretty sure that it's basically a way to be able to sell hi-definition DVD-audio discs to audiophiles and generate more interest in the so far totally unsuccessful push for next-gen audio while still letting the "holdouts" (meaning almost everybody in the world) play the discs on their regular CD audio players.
That is, it's not one side of CD and one side of DVD, per se, but a disc that has traditional CD audio on one side, and DVD-audio on the other, for audio nuts that want the superior quality. Only takes up one shelf spot, the added production cost probably isn't significant, and they're hoping that it'll get people saying "Gee, I already have all these DualDiscs, why not just buy a DVDAudio player and have my music suddenly sound much better?"
Doubt it'll do much good, though, as the conusmer market seems to be saying that people just don't care about quality that much--they'd rather get an old fashioned CD that they can still rip, ironically.