The rough can be pretty thick and tangly on the courses here, so if you hit a long iron just a touch fat it's going nowhere. The JPX 850 Forged long irons (4 and 5) have a slightly wider sole and larger face to help get through the rough a bit better and help a little on mishits (high or toe side). The PM Grind wedge is better out of the bunker and the rough around greens for me than any wedge I've used, so it's stayed in the bag for quite a while. I don't see it going anywhere until its replaced with a new model PM grind wedge. As for the MP-H5 2-iron, the head and shaft combo gives me the best results of any driving iron I've every used. It just works.
So, pretty much the reasons for the mix are all down to the experimenting and going where the results lead (backed by data from game golf).