It's not really necessary to be honest. I'm not really buying the whole length thing. I often quote many people I want to reply to in one post. Why would you need to double post? The only way I can see it being valid is if a thread hasn't been replied to and you need to bump it for whatever reason.
i often scroll through threads replying to each entry on its own (but i dont have any sig ad)
but imho you are right with the length of one post. i dont see a reason to split that.