First of all, it's 6.1 vs 4.4 this season. Secondly, it's the law of averages. 1.7 trips per line at a 78% conversion rate translates to 108 extra points per season. You think that might influence the final score of a game or five? Not to mention wins that it pushes out of reach of the opponent, could force them to take bad shots near the end of a game (a 5 point lead vs a 3 or 4 point lead), or gets the opposing big men in foul trouble. 1.7 FTA per game is a huge difference.
But your theory that WB gets to the line more because he's more athletic really falls apart when you consider just how athletic Parker is and then combine it with the above list. It just makes no sense at all.