[mileswu]

He could always sell his software via his own store, as Kindles are not restricted to Amazon App Store sold software (which is one difference between the Kindle/Android ecosystem and an iOS one).

[astrodust]

Then you're responsible for driving your own sales traffic, which is a lot more work than simply ending up in a category and getting drive-by sales.

The advertising cost wouldn't produce a positive pay-off for an app of that variety.