Rickochet
First question: It wasn't necessary for gapping purposes. Only the 3 and 6 in the set needed the "help" of higher COR for proper gapping. Remember, of the two lengths, those are the "longest" irons in the grouping. So the 3 iron is shorter than a normal 3 iron and the 6 iron is shorter than a normal 6 iron, so they needed a little boost in addition to the loft.
Second question: More forgiving, higher offset, heat treated hi-COR faces.