In gmail if you don't archive something it goes away on its own and it's lost. I've been using Instapaper daily for about 3 years and have always considered it one of my favorite iOS apps. I use the 'read later' folder for exactly what it is. A dumping ground. A sort of limbo. When I want to save things for an extended period I just move them into a different (non-readlater) folder. They stay there. Not only that, but they are categorized.
There are a lot of stories/comments on HN that I disagree with, but in this case I really don't understand what the problem is at all. Maybe I am missing the point because I'm not using a designated "archive" function and don't realize how much better it is. Is there a reason archiving is better?