Instapaper's an interesting case because, as Anil said, it's basically stating that UX on the web is shitty for reading longform articles. By stripping out the work that goes into layout (which, may surprise you, but journalists do take a lot of pride in how their work looks), users are rejecting the work that's there.
I certainly think this is a growing field, and it'll be interesting to see how advertising adjusts. I was in plenty of classes where we had BBC and Google employees talk to us about RSS feeds and properly serving ads, so I'm sure there's conversation around this.