I used to read George R R Martin. But I realized a _long_ time ago that Martin's love of killing off central characters was not something I was okay with (yes, I'm talking about the Wild Cards series).
Anyway. "According to first-day sales collected by Random House, more than 170,000 print copies and 110,000 e-book copies sold on Tuesday, the largest opening for a Random House book in 2011."
Let's think for a moment about what went into this marketing phenom:
(1) HBO series: people with the money for premium cable can presumably afford a book every now and again
(2) #5 in a fiction series when #4 came out in 2005 and entries of which have been nominated for and/or won most relevant awards
(3) The boxed set for 1-4 is priced at a significant discount to the kindle editions (at least online).
The HBO series is no joke; look what happened to Harris' Sookie Stackhouse after True Blood hit it big. It doesn't matter that only some of the people who love the series are going to enjoy and stick with the books -- a whole lot of them will give it a try.
But I think #2 is a big factor. If I were a George R. R. Martin fan (I'm _really_ not) and I had been buying the series all along, I'd have the first four in paper by the time my husband bought me a kindle. And if I were a big Martin fan and had any chance at all of seeing him at a signing or, say, Worldcon, I'd _really_ want all copies in paper.
And then, it's summer, so there's the whole vacation/beach reading factor: not relevant for a serious fan, but for the vacation reader at a loss for what to try who maybe enjoyed season one of the a Game of Thrones, nothing to kid around about.
It's tough times out there for bricks-and-mortar bookshops, if the big news in summer books is Martin.