I don't know, rejecter, the problem with so many agents and publishers is that you're interested in selling self-consuming artifacts (you went to Brown, you'll recognize that _expression) with a brief shelf-life. You equate sales with success. Stephen King had good commercial success with his early novels -- does anyone read them now? Buy them now? How about John Grisham? How about Wallerstein and Bridges Over Madison County (god what an awful book).
I read an interview that Andrew Wylie gave with La Monde where he described his method as trying to bring literature to the fore. He said that he pretty much despised Dan Brown and didn't care that 70% of the publishing world wanted more Dan Browns. There's an agent I'd give my left nut to have represent me, someone actually interested in literature and the contribution it can make to the culture, not only now but years from now.
First of all, Stephen King has had a lot of commercial success recently with both his fantasy Dark Tower series and his new horror/sci-fi novel Cell. He also writes regular columns for Entertainment Weekly. John Grisham's book The Innocent Man is currently #2 on the Amazon.com website in bestselling books. I can't remember off the top of my head if Wallerstein has written anything recently, but every writer has dry years and bad books. Some writers only have a certain number of books in them and either start producing crap or just stop writing pretty much altogether (J. D. Salinger, America's favorite non-writing writer)
In terms of equating sales with success, that's true and not true. The publishing industry is so tough that if you want to be a multiple-book writer, you have to have a significant early success, because you will be judged on the sale of your earlier material. If your first book is a flop, or doesn't do well enough to recoup publishing costs, your career with that publishing company is probably dead and the agent will have to take your future books to other companies, who will know that. For people who just wanted to write one great novel and get it published, that's not really an issue, but an agency can't have a giant list of one-book authors. It needs a stable of authors who regularly produce publishable material.
Most agencies have a varied book list. While the agent loves every book on that list, the public might not, and the agent is aware on this. A good agency (financially) will have a stable (and we do use this term) of authors who, like I said, regularly produce books (about every 1-3 years) that sell for significant advances (over $20,000). The stable will probably be relatively small, depending on how successful those authors are. One author can carry an entire agency for years. Then there's the others on the list, who aren't commercially successful, or are first-book authors who got a first-book advance (around $5000-7000), of which the agency got 15%. They get to stay on the list because the agency is floated by the stable authors, and the agent can afford to take on a new author who might have terrific material that just won't reach a huge audience.
For all of the criticism of agents representing what some people consider bad literature, nobody has bothered to inquire what other books Dan Brown's agent (if he has one) is representing.