Even if the wifi radio's firmware is fixed, it can still be made to do things that are illegal or anti-social.
Different countries have different wifi channel availability. I don't know what the US does, but I'm pretty sure it doesn't support channel 14 (Japan only?) for example. Does it support channel 13 even? The radio needs to, unless the FCC wants special US-only versions of the firmware with that feature permanently disabled. Otherwise the router can just tell it "you are in Japan, use channel 14".
There seems to be a desire to regulate 5GHz devices much more tightly than 2.4GHz ones as well. That makes sense - 2.4GHz if fucked because there are so many crappy devices with the power turned up to 11, using as many channels as they can grab simultaneously and generally being dicks to their neighbours in order to benefit themselves. No manufacturer will voluntarily slow their equipment down or reduce range just to place nice with the competition.
So 5GHz devices have more rules to follow, but it's too much for the firmware of low cost radios to handle. A key cost reduction technique is to offload work to the router's CPU, much like the WinModems of yesteryear. That means the router's firmware can break the rules unless locked down.