Wikipedia has a good rundown of something I hadn't been aware of in the music business - the tendency to mix up the volume of an album to compete with other records (particularly in lo-fi formats like radio where a "louder" record sounds better. Unfortunately, this comes at the expense of some of the dynamic range of the music, when elements that would usually define the highs and lows of the record lose their edge. I'd noticed that that the drums in many older recordings sound crisper - now I know why.
You know the annoying difference in contrast between television shows and commercials? That's the same thing - turning up everything in the mix so that even the quiet bits of tracks seem loud.
Dubbed the "loudness war," this practice began in the early 90s and is now practically the standard. I think that some albums have managed to sound good despite this tendency (mid-period Soundgarden and Faith No More records, for example), but it's never necessary - by turning the volume up on your stereo you can listen to a record at any volume you like without sacrificing crispness. In other words, this practice always results in inferior quality. Unforunately, I don't need another cause right now so I'll leave much of my righteous indignation up to audiophiles.
The Loudness War - Wikipedia
Rolling Stone article on the topic
27 minutes ago