Really, who made this rule that stand-alone chapters MUST* have a sex scene?

I did. It's in the Picture Reader's Guide to Writing Satisfying BL Manga, which was vetted and approved by the Committee on Yomikiri in May, 2007. We sent you a memo. If you're not going to attend the meetings...

How much is it killing me that Gakkou no Sensei was released two months too late for my order and its status at Amazon is currently "usually ships within 2 to 5 weeks." Don't make me come over there, Japan.