Chris Bryne explains a number of things that the music industry is doing wrong.
The Cliff Notes version: CDs are being mastered to make them louder resulting in a loss of information, those mistakes are being carried over into the compressed AAC/MP3/WMA formats and to add inury to insult they muck with the EQ levels so they sound better on portable players.
Go read the whole thing.
Having a music studio of my own, I can verify that this is correct information. Everything is run through multiple layers of compression these days. Most mastering engineers hate it, but that’s what the suits want.