Nobody ever said the gap in salary can be accredited to that difference. Take away those jobs and the areas where Stanford grads go, and they will still have a higher starting salary, just nowhere near as drastic as the numbers make it seem.
32% is a huge number compared to BYU. In my graduating class, I would guess that number is in the single digits at BYU. In our class of ~200, there were maybe 3-4 guys that went to i-banking, a handful to consulting firms (only Accenture, Delloite, not BCG, Bain, or McKinsey) and maybe one or two went to private equity. Considering most of those jobs are $150K+, while others are $90-135K, that would make a big difference.
Just to make sure you don't misunderstand, in no way am I saying that BYU and Stanford are on par with each other. Stanford is clearly a better program. But the difference isn't as big as the starting salaries would suggest.