My question is, what happens to someone who makes 9 posts in case (a), and 13 posts in case (b)? Is it fair to deny anyone who has made more than 75% post for the week? Could there be a somewhat reward for such people?
Well it all depends on the Campaign Rules, Managers and of course the "Rate". The higher the rate the stricter the rules are.
We're talking about money and employment here and we are all bound by the rules.
"If you can't abide by our rules, we'll find someone who can".
However, some campaigns does not have that stricter rules, I've seen someone not reaching the required post and yet he got paid and the CM doesn't terminated him. Some campaign managers give you chance to amend your shortcomings and some don't.
Just to be safe, follow every rules the campaign set for you to follow.