All manufacturers have their quirks. I could say that the EVO Shift should have had the same processor as the EVO 4G, but HTC had their reasons. The overall problem is, communication between the carriers and device manufacturers is not as good as it should be.
There was time for the 4S to have 800CDMA. Most Sprint phones in 2011 were given it. The EVO 3D was announced in March, which gave Apple plenty of time to integrate it, but they chose not to as an exercise of control.
On the other hand, if at&t had had their way when the iPhone 1st came out, it would have had 3G from the start, but Apple was in control, and at&t had no say. In essence, they were Apple's b***h, for lack of a better term.
And the reason that iPhone 5 supports LTE on PCS A-F, is because Band Class 25 (PCS A-G) is a superset of Band Class 2, and therefore, you can support both LTE bands at the same time.