For many of the current-release books that most interest me, I'm seeing a price difference of only $2.00 between the Sony store and Amazon. For example:
Now, I started with the bestsellers list at the Sony store. But looking at the no-longer-new-releases, it does look like the prices at the Sony store and Amazon are moving much more closely together.
Fearless Fourteen by Janet Evanovich is $15.37 at both stores.
The Book Thief by Markus Zusak is $7.19 at Amazon and $10.79 at Sony.