@@Strandly, you can't have a par 3.84. A hole can "rate out" at it though.
So you're saying the difference between course rating and par is simply due to rounding? Now that makes sense.
No. Think of it as the difference between rating each hole individually, and rating the course as a whole.
Take the earlier example of a par 72 course consisting of 18 340-yard, uncomplicated holes. At 340 yards none of them can be considered a par 3, they're too long for even the best players to expect to make 3 every time. So they all have to be par 4s, and therefore the par on the card has to be 72.
But because all the holes are straightforward, a good player will usually make several birdies. He won't be able to predict exactly where they'll occur, but over the course of a round he'll likely make four or five. So the rating of the course will be 67 or 68, becasue a scratch player will be expected to get round in that score.
Does that help?