In Australia the Kindle editions are priced at a 50% to 100% premium to the hardbacks. For example in Australia the kindle edition of "Blue Remembered Earth" is $20.07 and the hard cover is $15.
I'm told that in the US this is $12.99 for the kindle vs. $16.52 for the hard cover.
I guess its the cost of posting all those electrons over the intertubes to the other side of the world :-)
But seriously Alastair, how about flat pricing around the globe for the Kindle edition.