The driver is indeed "protected" for IP-lawyer reasons; they'll have it out under license to every Tom, Dick, and Jane looking to build a device with their chipset. The firmware, on the other hand, is very closely held, because that's where the chip's functionality lives. A WiFi chipset implements a fantastically complicated protocol, and no one wants to bake that into hardware that can't be updated as bugs are found; so they build relatively simple hardware, and slap a microcontroller right on the die that runs all the complicated logic.

This means that the microcode is as sensitive as The hardware specs on earlier generations of hardware; a competitor with a copy of that source can make a (perhaps better and improved) knockoff if they're not too worried about legal implications like, say, several dozen Chinese knockoff shops.