I have to admit, a tiny bit of my reluctance to announce verbally my intent to pass is an introverted inhibition. Most of you, and all extroverts, will find this silly, but some of you introverts may understand where I'm coming from. Seriously, I'm not trying to be an a-hole when I pass silently, and I assess each situation as they appear, so I will make a verbal announcement when it's likely I'd startle someone. And I actually prefer cyclists passing me to do so silently. If they yell something, I'll know it's because they've adequately determined the necessity to do so.
But I do know the law is the law, and most locales require an announcement when passing. You know, I'll follow that law when motorists stop blowing through red lights, which is enormously widespread now more than ever before.