Probably because, like most developers, he has separate development devices that he only uses for development. So he probably never ran into storage constraint limits while just testing Instapaper.
As an example, I have a 32GB iPod Touch that I've been using for all of the iOS5 testing for my applications and I'm only using around 600MB total. I'd never run into this issue either unless I loaded this up with tons of other apps and movies and music.
