Just to clear up any confusion we may have, quests do not give just the gains listed on it's post. When you do the quest you get the gains you would normally get from a post of that size PLUS the gains listed.
So, example:
Cyril does a 500 word quest
The quest's listed gains are +100 PL
He gets roughly 400 PL plus the 100 PL
So in total Cyril gets 500 PL.
Everyone clear? Good.