mp3s are not good substitutes for CDs

While the RIAA continues to blame falling CD shipments on Napster, Soundscan (that tracks retail sales) says CD consumption is going up. The best evidence, to my mind, that CD sales have not fallen as much as the RIAA claims is that CD stores do not seem to be closing down in the vast numbers than a 10% decline in sales would suggest.

I do not understand why mp3s are not a better substitute for CDs, but I can't find evidence that they are. For me, I buy the same (small) number of CDs I used to buy before -- my mp3s (on my iPod) substitute for radio.