Well, as far as I know, there's also no rule, anywhere, that suggests that there IS a difference between "making a casualty" and "removing from play". In other words, there's not an ability that says "remove the model from play, but don't consider it a casualty", nor is there an ability that says "this only works if the model becomes a casualty and not if it is removed from play by other means".
I'm sure there are other examples of slightly different words being used to the same concept as well, like "Suffering a wound" and "taking a wound", "rolling for difficult terrain" vs. "making a difficult terrain check", etc. True, nobody has a window into what GW really means, but subjectively, my take on it is: assuming there must be a difference between casualties and removal from play is reading intention into GW's words that isn't implied by the words themselves, and furthermore, it makes the rules a lot more complicated than they need to be and raises unanswerable questions about WHICH removals from play are casualties.
And OK, we've now all officially thought about this way too much...