At some schools yes, but as other people on SDN have pointed out, every school is different. Other schools may have it as a custom that once applicants get to the interview stage, they are all on equal footing (blind interviews, for example). It depends, and trying to demystify it is pointless. Just be happy if you get an interview, do your best and then don't sweat it. The whole point of this application process is to do what you can and make THEM reject you, instead of you rejecting them by not putting enough effort in or something. In terms of sports analogies, you want to keep the ball in play by always putting the ball back in their court. One misstep -- you may shank it or be able to recover from it. Sorry if that seems vague but it's the best way I can describe this process as far as I know of it thus far.
Just do your best on the interview and be mentally prepared that while you did acheive a significant step by getting to it, an acceptance is by no means in your back pocket, no matter how you think you did.