I don't know specifically which ones might apply to iPhone, but there are laws in the field I work in where radios cannot be operated near designated airfields or offshore, forcing us to add GPS when we would otherwise not have. This would also be consistent with reports saying this only occurs on the newest iPhones that have additional radios than before like ultra-wideband. There are other laws like E911 reporting which may also apply.
Now regarding why there isn't a more concrete explanation from Apple: Krebs might have published before Apple was willing to make a statement; Apple may not want to commit to this being the only use of location outside a user's explicit control in system services; or Apple might believe uses like this are fine for the system because they aren't harvesting data off-device, and they want to continue having this ability.
Since the global location services switch works as you'd expect, I think there are a lot of good faith cases to be made for Apple here. Given their secrecy, we won't know for sure, but their statement seemed to suggest that they were confident this was an acceptable use.
