I think Readability's model is a little presumptuous. Why do they get to decide unilaterally that they deserve 30% of the revenue? It's not like the App Store where you agreed to it. Given all the work that goes into creating an article, is extracting the text worth 30%? If I was a publisher, I wouldn't think so.

To me, Instapaper's approach is much more straightforward. You have to have gone to the publisher's site in the first place and seen all of the ads. You pay a flat fee for the Instapaper app, and can subscribe if you like the service. Why make it more complicated than it has to be?