I suspect part of it is that they didn't want to "hurt" the Ducks' chances. No word on whether the tactics of a player like Brown hurt the Wings' chances. Franzen's postseason struggles last season were largely caused by a blow to the head. The Wings were lucky. (Feel free to look up any number of NHL players who were forced to retire due to head injuries. I would guess few, if any, were the result of legal hits, because, you know, it's illegal to hit someone in the head.)
That's why you have teams like the Ducks and Flyers. Why bother to follow the rules if you don't ever have to pay?