Halo 3 had superior graphics, a matchmaking system, and near-infinite custom games. While Combat Evolved was not a bad game, I can think of no aspect in which it surpassed Halo 3.
Well that makes sense, seeing as how it came out 6 years later. It was a great game when it came out...which is when people played it. So it would make sense that people would remember it as one of their favorite games.