Only blockbusters need apply

The publishing industry is pursuing the big block buster book deals, offering authors six figure advances, and doing massive publicity campaigns to sell the expensively advanced book. Result?
Fewer books published. As a book buyer this is an unpleasant trend, reducing the number of new books in the stores, and limiting them to "mainstream" fiction. Many readers don't like mainstream fiction, they perfer genre fiction or history or biography. It also chokes off the supply of new writers. Few agents or publishers will talk to a first time author attempting to publish his/her first book. That trend goes way back. Best selling author Tom Clancy finally got his "Hunt for Red October" into print via the Naval Institute Press, after the ordinary publishers turned him down repeatedly. If the publishers won't publish first time authors, eventually their stable of published authors retire or die, and then what's to print?
Could this concentration on block busters be responsible for the overall slow down of book sales? Something like this happened to the CD business. The suits running the music business have failed to find new singers, and CD sales have been falling for years now.