"Wasn't Rush Limbaugh's first book the biggest selling book other than the Bible?"
Not sure, but I doubt it seriously. With books such as the 'Harry Potter' series, 'Gone With the Wind', and many others having a wider audience.
A quick Google search shows the 'Quotations of Chairman Mao' coming in at #2 - Rush didn't make the top 10.
I think you are mistaken about Rush. I remember his books making #1 on the NYT Best Seller List.
Sorry, but my google search function has been freezing my computer for several days now.....