Further testament that the iPhone is the idiotPhone. If SIRI was locked by default, most people probably wouldn't have a clue how to unlock it if they wanted to, let alone even knew it was possible.
Oversight by Apple? I think not.
Oh yeah and don't be an idiot and leave your cell phone laying around for others to use it, either. You never know what charges you might incur or worse, what they might be doing with your phone. If I had an iPhone (which won't be happening), I wouldn't leave my phone around so someone else can open up the Pod Bay Doors.
I can hardly wait until a criminal gets caught using SIRI by finding a location to bury a dead body.