Hence why I included the part "you can't get close to them (unless they're completely stupid)." If they're standing 15 feet away from me, I really have no choice but to get on the ground.
Actually, you can cross 15 feet fast enough to beat reaction time. People who are trained to secure possibly armed assailants make sure to keep more than 15 feet as this distance can be covered quickly. Now, usually this time includes drawing your weapon. However, charging an untrained person with a handgun is entirely possible at 15 feet. Not that I would recommend it.
The point I was making though was one of "usual distances." If you are getting mugged, you are in close quarters.
I'm pretty sure you don't need training to get out of the way of something and run.
That isn't an option in close quarters where most of these attacks take place.
Even those who are trained to disarm an opponent are taught that your best chance for survival is to avoid conflict and just give them what they want.
Not true at all. For example, my Krav Maga training centers around responding to the threat immediately and forcefully BEFORE the person can use there weapon. Disable them and get away.
If it's not enough to satisfy them, or what they want is something you can't (or won't) give, then it comes down to fight or flight.
And if it comes down to that, I want a gun. It is an excellent preventative measure.