MLeake: The fact that most LE officers today carry semi-autos does not mean that a wheel gun would be ineffective for civilian self-defense. Wheelguns did the job for a very long time and continue to be used effectively today and likely into the future.
As for the probability of a criminal's response to deadly force; yes there is always the possibility that a drug crazed or mentally disturbed individual will continue his attack after being hit. But the vast majority of criminals are cowards, who seek easy prey. I am retired now, but have many years of experience working with criminals, trust me on this one.
The below video has been posted on thefiringline previously but is appropriate for this thread.
http://www.youtube.com/watch?v=Ey11D4wzxHE
The response, to two rounds fired by a 65 year old woman, by these five would be robbers, is typical of the vast majority of bad guys I have dealt with over the years. Most criminals are only brave when they believe they hold the upper hand.