While it's nice to argue that the subs were originally in the image area in theaters, the truth is, putting them below the picture wasn't exactly an option for them.
Until there is such thing as a 2.35:1 television, I personally prefer subs in the black borders than overlaying (and obscuring) the picture.
Heck, forced soft subs is even more preferable since it saves bitrate for compression and you don't have to worry about artifacts from the text's edges.
That's just my preference, but everyone is different. It's just one of those things that I don't feel strongly about preserving from the theater. It's just subtitles FCOL.