You never see popular culture mention Supergirl on anything. At all. They always mention Superman and his myth in Seinfeld, Big Ban Theory, movies, songs, mass media, etc. Why? Because he IS the icon.
General audiences know it all started with Superman. Supergirl wouldn't exist without him. Superheroes as we know it wouldn't probably. If WB want to go ahead and crap all over the Superman mythos for his spinoff then I have zero respect for them and I find it hard to believe that DC Comics would let them do that...