The one that I mentioned intervain is because like a case in stake signature campaign on bitcointalk, there was a time where the community call out the rules of the campaign and which brings much spam on the forum and despite strong defense the manager yielded to the pressure and changed some rules in the campaign.
Although the manager has every right as we have observed with a few managers, not every one of them likes comments aside from applications on the signature campaign page, whatever discussion or requests are better entertained via PM.
Yeah, it isn't very pleasant since the thread got bumped, thus giving a false sign about new slots opening (or whatever) like on the BTCT chipxxxxx campaign. At the same time, if users cannot freely post, then there's concern about the legitimacy of the campaign. Many times, users have tried to give a heads-up about a campaign being a scam, fake, forum abuse, etc. IIRC Stake is one of the good examples I think (about abusing forum), not a bad one.
1. Make it self-moderated. I don't see any reason for the campaign managers to delete application, but in deleting some posts that would clog the overall thread is.
Self-mod isn't applicable to signature ANN IMHO since it can be abused by scam campaigns or any problems that arise about payment.