Amazon Sez . . .
Several grains of salt need to be taken with this message. No raw numbers are provided, only a percentage (143 Kindle sales for every 100 hardback sales). It's not clear how many of the Kindle sales replace hardback sales, and how many replace paperback sales. A great many Kindle books are out-of-copyright classics on sale for 99 cents or for free. (I just downloaded the six-volume Decline and Fall of the Roman Empire for my Kindle, and it cost me less than buck.)
And of course, Amazon's figures have always been notoriously slippery, as any author who has tried to track his own Amazon sales will tell you.
So the barricades have not yet been stormed, and the revolution, whatever it is, has not triumphed.
Still, this probably means something or other. Your guess is as good as mine as to what.