My TV has a black stripe at the top and the bottom when playing blue ray movies. The picture looks great but i thought blue ray movies had the whole screen?? It kinda looks like a dvd widescreen movie.
If the BluRay disk is a HDTV show like "Weeds", "True Blood", "Terminator", etc - the video was shot in exactly 16:9 which exactly matches your TV.
Movies shot for the movie theater are done in at least 9 different ratios. (And in the case of Dark Knight - IMAX scenes are slipped in).
Do you remember when Movie theaters had those red velvet curtains around the screen? The would move them in or down to frame the different images. So movies always have had the black bars.
If this bothers you - your TV often has a "Aspect" button to expand the image.