What do book editors do?

Sometimes I wonder about this. I'm an avid reader and in recent years I've been shocked and disappointed in the quality of a lot of the books I've read. Misspelled words, poor grammar, missing words, awkward phrasing that needed an experienced editor's touch. Now we have the big flap about James Frey's books--it sounds like a government coverup: What did the editor know and when did he know it? The editor claims he was victimized by the author, denying responsibility for the false material published in both of the books he edited by Frey. This is a turnaround from his original take on it. The author is jumping through hoops, too, trying to save face, but too late, as far as I'm concerned. Everyone was saying that it isn't the responsibility of the publisher or editor to vet the book to assure its truthfulness. Excuse me? Well, at least Oprah did the right thing. Her apology to her viewers and readers seemed sincere and appropriate to me. I haven't heard anything even close to that from the author, editor or agent in the Frey case.