If it is just because the approver at the time does not recognize it as a troll, I would agree with your suggestion.

I guess that, and the different ideas of what a troll posting is are the two main reasons. But since I'm just one of many approvers, I can't really tell.

I think approval possibly needs to be looked at. It's very easy for one person to approve something, and impossible to unapprove it, without going thru consideration, which takes a while. One monk can (intentionally or unintentionally) approve a troll node, giving the troll what s/he wants.