I don't think there should be Yet Another Option for this, because of Yet More Options and because many people aren't even aware that this "number of posts" text exists and so it would be difficult to make it obvious what the option did.

I am, however, in favour of giving different information, so as to give an idea of the activity of the account while not offering an easy way to see whether hidden entries have been made. There are a few different suggestions on how to do this above.