Why is it important to know if an album was released by an RIAA member or not?

That's possibly a fairly long answer, but just the highlights of the RIAA's practices involve price-fixing, blaming its poor financial state on unfounded digital piracy claims (and in turn, blaming its own consumers), lobbying for changes that hinder technological innovation and change copyright laws, underpaying the artists it represents, invading personal privacy to enforce copyrights, and dismantling entire computer networks just because of their ability (of their users) to share copyrighted files.