The roots of creation

Does it matter why an author writes what he or she does? Or whether it reflects something in their past? And would knowing that improve the book for us readers?
In The Shakespeare Wars, which I commented on recently, Ron Rosenbaum thumbs down the idea. He dislikes the idea of “explaining” writing by looking at an author’s life, arguing that the work on the printed page (or the stage) is what we should be studying. Doubly so in the case of Shakespeare, where we have next to no information about him.
As an example of how not to do it, Rosenbaum cites one writer’s theory that Shakespeare saw a Jew hanged in London and was so horrified by the bigotry of the crowd he wrote Merchant of Venice as a rebuke (I’d agree with Rosenbaum that it’s nothing of the sort—no matter how you dice it or slice it, the anti-Semites in the play are the good guys). As Rosenbaum points out, that wouldn”t change the play, even if it were true (and we have no proof it was).
The best counter-argument (read some years previous) was from a literary historian who argued that rejecting the biographical approach was a way for critics to defend their turf: Never mind the details of the author’s life, look at his writing! Nothing else matters!
I tend somewhat toward Rosenbaum’s view. I do think author biographies can be interesting, and they can explain a lot—but I agree with Rosenbaum that if you have to know the biography to make sense of the book, the book is seriously flawed.
Take Orson Scott Card. A great many of his stories (Hart’s Hope, Songmaster, the early Alvin Maker books and Ender’s Game, among others) focus on a gifted child whose talent is as much a burden as a curse. Quite possibly this represents something in Card’s past; then again, it could be he just likes a child under pressure as a central character. I’d be interested to know—but it doesn’t change the books. Knowing Card’s decisions come from life rather than creative choices (I’m simplifying the alternatives here) wouldn’t make the books any better or worse.
Another example is “Pierre Menard, Author of the Quixote,” a story by Jorge Luis Borges in which Menard sets out to write Don Quixote—but even though he’s writing exactly the same book, he has totally different intentions for his work than Cervantes did so in the eyes of critics, it’s a totally different (and superior) novel (note: Borges is mocking this view, not endorsing it). It’s the same logic by which if Shakespeare were someone completely different, the plays would be different.
Also, I can’t help thinking that some of the impulse to “explain” authorial choices is less about true understanding than the inability to accept that we writers sometimes just pull things out of our butt. One of the standard scenes in old biopics about composers has the protagonist sitting around hearing birds tweet, horses clomp or rain patter—and suddenly, the sounds are the basis for his new symphony/waltz/concerto (brilliantly parodied in the PBS special Norbert Smythe: A Life).
Likewise, Dreamer of Oz shows L. Frank Baum creating everything in the Wizard of Oz based on real experiences—a bully who turns out to be a coward inspires the creation of the Cowardly Lion for example. In A Beautiful Mind, John Nash is shown coming up with his concepts of game theory by watching his friends hit on girls.
Some of this is dramatic convenience—having sit around and think is kind of dull—but I wonder if doesn’t indicate an underlying inability to understand creativity; the story of Newton getting hit by the apple goes back well before Hollywood. It simplifies what can be a fairly baffling creative process, even for creative people.