What is so wrong with the passive voice? Wikipedia suggests it goes back to Elements of Style: "In a sentence devoted to explaining why it should be avoided, The Elements of Style itself employs the passive voice[7], concretely showing the utility of this grammar feature, despite prescriptivist ideals." HA!

Passive voice is not always the wrong choice.

However, a passive-voice sentence can usually be rewritten to use fewer words, by making it active. Usually, if you reduce the number of words in a sentence without changing its meaning, you've improved it. This is especially true for things like slogans and taglines, where cutting out even a single word can make worlds of difference.

I think that's why Strunk & White recommend avoiding passive voice.

To summarize:

Shorter is better.

The passive voice is often used to evade responsibility. For example, "Mistakes were made" doesn't say who made the mistakes

But in your example Bruce, using an active voice just focuses more on playing the blame game, as opposed to using the passive voice to focus instead on, for example, the best solution and what to do about the current situation. Which, in the long run, is accepting responsibility for what matters most.

Usually, I have high regards for concision, but in the case of this particular slogan, the intended nuance suffers. You're reading along, "HP is protected...." and you're thinking, you know, "hey, I work for a big stable company, it's all good, lots of protection around here, someone else must be on it, his job not mine, so I can relax--" but then all of a sudden you get to the end of the phrase, "by YOU", and it hits you. You enter a paradigm shift, and come to the realization that your own actions play a significant role in representing the corporation's integrity.

You don't really get to experience all this with the more desperate "You protect us" because you'd read that like, well I have a lot of other important things to do too, and there's nothing particular that I do every day to-- actively-- protect HP. But by employing the passive voice-- and YOU-- HP is all the more difficult to penetrate.