We are in a very competitive public school district in California. One of my friends' daughters just got into MIT. She is a real math whiz. She skipped pre-calculus and took two years of AP Calculus (AB and BC) at our high school, then took an advanced calculus class at our state university her senior year.
Several of her friends skipped AB Calculus and took BC Calculus. They said that was "really hard." (hard to skip AB and go into BC).
If 4 years of math aren't required to graduate, my son still plans to take 4 years since he wants a math/science career.