Hey TRUFLARE-
From what I understand, it is certainly possible to not get an interview invite, but still be considered for admission, sometimes without interviewing at all! I think this is pretty uncommon, but it goes back to the whole probability thing: if a professor interviews 5 people for 3 slots...and offers 3 people admission- what if those three people have turned down the offer because the've received an offer somewhere else? And what if the two alternates who were not originally offered admission, too, have turned down the offer? Then they have to go to the pool of applicants. At some schools, they have waitlists for interviews, so, if you haven't been put on one of those but you know a school has one, you probably won't be in line to interview. But say there was no waitlist of applicants to interview, then they have to dig back into the pile (however organized or ranked or selective that pile might be).
Unfortunately, it can sometimes also be the case that if you've not received a rejection, but not interviewed either, sometimes it's just an oversight and they have left you off the list of people to contact with rejections. But anyway, don't give up hope. I know people who were waitlisted and accepted without interviewing during the regular process. You never know...