Also on Kindle…

I've noticed with increasing frequency the option to purchase long form articles for the Kindle. It's always just a click away, and presumably offers better formatting than simply using something like Readability's "send to Kindle" button (as well as a nice cover, occasionally!).

I can see why a writer would love to offer this option, but I can't really understand what would compel a reader to spend a few bucks per article when the article is already free online. Does anyone out there have experience with this from either end of the transaction? If so I'd love to hear your thoughts.

[Here's an example, and I've also seen some of the longer Verge features offer this.]

Update: Another appeal would potentially be to financially support a writer that you appreciate.