Based on my limited experience I believe the insistence of the major publishers on agented submissions is a disservice to themselves and their readers.
Magic Bullet Q&A for Writers
How polished does a manuscript have to be for submittal, or do they still have editors that work with the writer?
Q: My question concerns getting that first novel published by a good firm. From what I've read, the critical first step is finding an agent who knows all the right people at the big houses, so I'm wondering how one gets taken on by such an agent...