The 1,000 character limit is useless, yes.

But the 20 posts per day? I don't know... I find it quite useful actually. If someone can't make its point in 20 posts in a day, then it means that person failed at arguing and should probably stop writing for the day.
It's a forum, not an irc channel.

The case where someone wants to participate a lot in various subjects and subforums is quite low... or that person likes to get involved in everything for no reason.

So, yeah.... even if there are downsides to it, I quite like the upsides of that daily limit.