First, it's Strunk, not Stunk.
Second, "Elements of Style" is a guide, not a set of absolute rules. Sometimes the passive voice is appropriate. Sometimes a bit of verbosity is in order. But I have yet to see the RPG book that erred on the side of brevity--not even 4E. The 4E rulebooks may not have had
much prose, but the prose they did contain was just as overblown as stuff from earlier editions. Take the flavor text from 4E Sleep:
"
You exert your will against your foes, seeking to overwhelm them with a tide of magical weariness."
It's just one sentence, and it
still manages to be twice as long as it needs to be. Compare:
"
Your foes become drowsy and sink into magical sleep."
Half as long and just as flavorful. Every RPG book I've ever read would benefit from the ruthless application of Strunk and White. Worrying about applying S&W too ruthlessly is like worrying about obesity when you're distributing food to famine victims. Yes, it could in theory become a problem. No, it should not be high on your list of concerns.