But I have seen the serious-posters suggest that interruptions aren't permissible.

Not *all* serious posters (at least, I think I fall under that heading)! I stuck up for the right of anyone to make their own responses to serious threads.

aybe I'm missing something, which is quite possible, especially since I'm not an Avon Luster... But I've not seen Avon Lusters request that other fans not interrupt their threads. They may not like it.

Actually, most of them seem to take it very well. After all, Tarrant-lusters and Travis-lusters often interrupt Avon-Lust to promote their own favorite. A.S.K.S. members have been known to try to put an Avon-lust thread into their own spin, which is an emotional/mental kindred feeling. Neither of which I've seen done for a while, but it never caused any trouble that I remember.