I'd have to agree with the OP, you're not overthinking it at all. Most people tend to pay attention to one thing, and one thing only when they're standing at a urinal or toilet... Situational awareness goes out the window. Using a stall is safer than using a urinal for the simple fact that a mugger/assailant has to go through the stall door first to get to you, instead of just coming up behind you and jacking you like what happened to Rusty's friend. Using the stall instead of the urinal is FAR from overthinking it, it's being safe and acting to prevent the lapse in situational awareness from being capitalized on by a BG.
@mcdonl: If you don't allow carrying a deadly weapon to affect every part of your life while you're carrying said weapon, then I would advise you to take another concealed carry course, or some personal defense courses... A public restroom is no different than a public street or store or anywhere else that you may be carrying. Do you imply that one is immune from attack while in the restroom, or that there's no use defending against an attack in there? From there we move on to why bother carrying if you're not going to maintain an awareness of your situation and circumstances in order to know whether or not the firearm is required?
I'll be the first to admit that I'm not 100% aware, 100% of the time but when I'm carrying a firearm, I do everything I can to keep from having to use it, and that includes pissing in stalls and paying attention to what's going on around me, even in the restroom.