I know there are various ways to get/replace album art in iTunes and other questions about that. Some of them don't provide as good quality art as from iTunes (Store). Some of them also inflate file sizes by putting the image in each album. However, one thing I've noticed is that sometimes art gets updated in the store to better reflect the CD I ripped, or missing art becomes available. For example, Bob Dylan albums used to always get the ugly "Bob Dylan Collection" cover (same for each) whereas now they get the real original covers.
Is there somewhere to report mistakes and omissions to the team responsible? It seems that overall quality could easily be improved if Apple accepted "bugs" on this. The mistakes often seems quite strange - for example, the album is in the store with the correct artwork and yet you get the wrong art downloaded or none at all. I recently got correct art for an unusual independent artist who I thought had self-published his album, followed by nothing for Phil Selway's much more famous new album. This album is available (correct art) in the store!