Ask PG: Why did you disable iframe viewing of comments?

Hi PG, I use the excellent Hacker News reader by Josh Huckabee every day - http://hn_reader.joshhuckabee.com and a few days ago it stopped displaying comments of HN stories. After getting in touch with him he says there is now a new HTTP header preventing HN pages being displayed in an iframe. Can I ask why this is and whether it would be possible to reconsider that decision? Part of the beauty of HN is that even if someone doesn't like the format/design, there are a myriad of other ways of accessing it. Especially only being displayed in an iframe, it wouldn't be placing any extra load on your servers right? I would really appreciate it being looked at. Thanks!