Not really - you have that mixed up with matte boxes - those shouldn't be visible under ideal conditions but the matte-lines were always there (not in all shots - depending on how successful the compositing was).

Look how completely different this digitally recomposited shot looks for example:

And yes, the new composite does look better/more realistic, but so do the new digital matte-paintings and some people might argue, that CGI Dewbacks look better than immobile rubber figurines, so where does one draw the line? The above shot shows quite clearly, that re-compositing a shot digitally is definitely altering the original shot in a major way.