The difference here is that when the king heard about this abomination, he summoned an army of 400 and scoured the countryside for the offenders. In the case of the "civilized" Aztecs, the king also scoured the countryside, but for the same reason as Sawny Beane: shopping.
Yes, I know. I wasn't drawing a parallel between the two. It's just that - let's face it - how often do you get to bring up the Beane family in the course of a lifetime?