I'd choose either PLU or UW over Pepperdine if the money were the same! The extra money would just be a bonus.
Is there something I'm missing, or is it simply the lure of the beach and lots of three-quarter-naked women?

(I half apologize, only because I fail to see what your son thinks makes Pepperdine so attractive? Are there programs there not available at the other schools? Is the quality of teaching in his field of study so superior? Are the documented outcomes markedly better?)
(The sibling thing: the college for my younger one is going to cost between 4X-5X that of my older one, and she will end up with some loans - though not overwhelming ones. She requires a different education than my older one, and brings different things to the table. She offered to go to a place where it would cost us less, and we wouldn't hear of it. But if the financial aid had been much less, we would have gone that route, and with no regrets.)