The page Wikipedia_talk:Non-free_content/Archive_43#Licensing_of_modern_French_buildings clearly states that an image can be free and non-free at the same time. It is important to state both licensing statuses. This is how French law works, and it is factually wrong to say otherwise. If you want to ask more about it, then please start another discussion on WP:NFCC. I did my part by starting the discussion archived on part 43.
 "sorry, but you don't get a "free" non-free image to show the company headquarters" - I have explained how French building laws work. There is no other way to show the company headquarters.
 "Unless the appearance of the building is of particular significance" - Ironically that is precisely how the architect copyright occurs. If the building's appearance is truly utilitarian, then the architect copyright does not apply. But if there is some architect creativity in the building, then the architect copyright does apply.