I was thinking that normally not everyone makes it to the Champion, that it's really rare, since the Elite Four are supposed to be really strong.
Plus the Champions seem to be the uh.. figureheads? The leaders? The creators seem to put a lot of effort into the Champions, since they're the final game ending battle. The Champions are also more involved in the story than the Elite Four, most of the Champions appear outside of the Pokemon League in the games. We know their personalities because we've seen them before, rather than having four lines of dialogue and a sprite.