It seems that Alistair Reynolds hit the jackpot recently, when British publisher Gollancz offered him a ten year, ten book deal worth £1 million. When I first heard of this deal, it immediately put me in mind of Steven Erikson, who in 1999, signed a nine book deal with Transworld, worth £675,000.
It used to be that large multi-book deals were a staple of the mainstream publishers, a trend that fell away to the point where new authors can only expect one book, and if that does well, provisional two or three book deal. In the book "The Perilous Trade: Book Publishing in Canada, 1946-2006," Roy MacSkimming made reference to a practice publishers had of shepherding talent, giving them time to mature, and time for audiences to find their books. The mainstream publishers felt that readership built slowly, and there was little point in investing in any author unless it was for the long term.
Today that attitude has disappeared...except for genre publishers. Unlike contemporary fiction, where multi-book stories are relatively rare, genre fiction depends on the extended series. The trilogies, the decalogies, the 22 books and counting runs where readers can once again spend some time with Detective X, or go on another campaign with a daring space ship Captain who had won their hearts fifteen books earlier. For every Stephen King, who has built a career mostly on stand-alone novels, or Harlan Coben who has mostly done the same, there are five to ten successful series authors, people like James Patterson, J.K. Rowling, or David Weber, who cater to a very large, and very voracious fanbase all waiting for the next novel in a certain series.
For the author who is lucky enough to land massive deals as Erikson and Reynolds have, it must seem like winning the lottery. But from the point of view of the publisher, such extravagance may actually be a smart and conservative move. Give your writer enough money that they can live comfortably enough that they won't have to rush about on side projects just trying to make ends meet, and that writer will supply you with a steady stream of books that can be marketed to their fanbase, then packaged, and resold abroad.