well done on totally misunderstanding the point being made.
yes all TVs are generally 16:9. but there are other ways of using an appletv.
as said, the black bars are not part of the video stream.
having to suddenly reconvert every video to make it a 16:9 stream just to facilitate being able to put subtitles slightly lower is absurd.
i would suggest it's a minority that would care to want to have the subtitles slightly lower.
do subtitles need some work, yes. is forcing all content be in a 16:9 container the solution, no.