The problems with having two different permissions are just too big and cause
huge queries, if they are granted differently. Also it's quite hard to decide
what should happen when a moderator has only one permission and the topic has
only posts of the two hidden types. To avoid all this, we merge them so it's a
simple switch: either the user is a moderator, then he can see all posts,
or he is not, then he can only see approved ones.
PHPBB3-9567