It isn't mandatory, but it certainly helps when you can pay for private tutors or professional consulatants that craft your application package. Students that tend to score high on SATs tend to come from higher income brackets. It also hurts when you attend a school that doesn't offer an expansive list of AP courses, or if you come from a family that never attended college and do not even know what the college process is like.

Edit: To your "This is patently untrue" comment. Taking AP courses and scoring 5s on the exams is pretty standard for applicants getting into elite colleges. By not taking those courses you are huritng yourself when applying to such places.