In regards to 2) above, many publishers do include this information. It's called "CIP" (cataloging in publication, I believe). Many of the cataloggers that I've known scoff at using this info though--it rarely meets their needs. University libraries often adopt the Library of Congress classification while public libraries commonly adopt Dewey Decimal classification. Even within each classification there can be room for disagreement or "doing it differently" for reasons that are relevant to your library, but not necessarily relevant to another library.
Disclaimer: I am not a librarian, but I worked in library automation for 18 years. The libraries that I worked for were all OCLC members. I've never catalogged, but I have loaded MARC tapes from OCLC and worked with cataloggers over the years. A good catalogger is anal-retentive, detail-oriented and cares very passionately about their work.
Yes. OCLC is a 501(c)(3) public charity. You can view their 990 returns in a variety of places online like guidestar.org.
A "non-profit" mostly can't sell shares nor link pay to profits. Many can do a lot of things that doesn't fit within the normal thinking about what a charity should do though. OCLC looks like a sad demonstration of that.. buying up competitors, screwing people on licensing, etc.
1) This sounds very similar to Gracenote and CDDB, but Gracenote wasn't non-profit.
2) Why don't the publishers include this information as part of publishing the book, so libraries don't need to dig around for the data or correct it?