Ars Technica:

To highlight work done to improve the sound of compressed music files, Apple recently launched a “Mastered for iTunes” section on the iTunes Store.How does this work? Ars spoke with Masterdisk Chief Engineer Andy VanDette, who recently completed a project remastering the bulk of Rush’s back catalogue. As part of the process, VanDette created special versions of each song specifically for uploading to the iTunes Store.

I bet you didn’t realize the effort that goes into creating music for the iTunes store.