If you ever tried to explain Instapaper (or any other read-later app) to a “straight” (non-nerd) friend or family member, you’ll know why Apple added a reading list to Safari. Even without the terrible experience of adding a javascript bookmarklet to Mobile Safari, Instapaper requires way too many steps: save page; remember to open Instapaper before the internet goes off to load that saved page; remember to read.
Safari, on the other hand, just saves the page inside Safari. That’s it.
And so Amazon is now simplifying Instapaper’s Send to Kindle feature, allowing you to send a web page to your Kindle with one click.