The FCC does care what modifications are performed by end users on licensed devices. these devices are licensed, by the FCC as 'part 15' devices which allow NO modifications of the RADIO by end users (not even extended antennas). they must be used exactly as licensed. modifications of the non-radio portions are not a problem. broadcom and other provide 'blobs', in part, to comply with this. If you modify the radio, by putting on a big transmitter say, if the FCC catches you(big if) you will be subject to civil and/or criminal penalties. Based on research i did to repurpose one of these i suspect the following:
broadcom radios and ethernet are weird, and so the drive has no access to the hardware per se, or even to a hardware interface as we expect it. rather the 'blob' represents the executable code for several processors (perhaps 4 or more) on the interface card. it is downloaded to the interface at initialization time. the interface cpus talk to hardware at a very low level/hardware specific manner and timing is important, foul up the timing and you can be transmitting on a different band or with unacceptable distortion. I believe there are several older mips cpus controlling various bits of the radio and directly generating various waveforms needed in the radio. the kernel drivers essentially IPC to one of the cpus on the interface, and it talks to the others, or modifies the control structures they use directly.
even users with special FCC licenses that allow development of devices for other uses under other parts of the
FCC regulations (re-purposing 'commercial off the shelf' equipment) can not get the code, i have been told its really a mess and not easily modified, small local changes can changed timings and effect other things. Ubiquity provides better support. Atheros provides some support, and a more reasonable hardware interface.
