The problem is that the Harry Potter movies are rated PG13 in the USA, and for a generic broadcast television commercial, advertising at the PG or PG13 level is a cultural no-no, regardless of what the element is that pushes it up to such a rating (violence, sex, language, etc).
And having worked with both Aussies and Brits, I've become sensitive to their respective cultural idioms and what's considered the limits of acceptability. In this regards, the USA is closer to the Brits perceptions of acceptability than the folks from Oz.
Overall, perhaps a better question is how much does the commercial's intended message really change if the "bloody hell" phrase hadn't been used? To this question, I think the answer is "Not Much". YMMV.
Of course, I am setting aside any cynical observations as to how one might purposefully chooose to create controversy in order to get some additional free advertising mileage.
-hh