Believe in One, Believe in None?

Here's a fascinating passage from the always thought-provoking Salman Rushdie (from the short story "The Shelter of the World"):

"If you were an atheist, Birbal," the Emperor challenged his first minister, "what would you say to the true believers of all the great religions of the world?" Birbal was a devout Brahmin from Trivikrampur, but he answered unhesitatingly, "I would say to them that in my opinion they were all atheists as well; I merely believe in one god less than each of them."
"How so?" the Emperor asked.
"All true believers have good reasons for disbelieving in every god except their own," said Birbal. "And so it is they who, between them, give me all the reasons for believing in none."