A washer manufacturer might have only two alternatives to comply with
the law: either go through a bothersome, well-documented physical
analysis process to demonstrate that a vacuum breaker wasn't ever
going to be needed, or just go ahead and install one. By doing the
latter they'd eliminate any possible conflict with some jurisdiction,
somewhere, which has a code that absolutely requires a vacuum breaker
on any clothes washer.

A thorough, practical analysis of why there's a vacuum break on every washer,
whether needed -- or not, and whether it serves a real purpose (other than
employing repair personnel when it leaks) -- or not.

Thanks!
--
John English