For high-profile ones, the only example of a quasi-successful confrontation I can think of only through sheer luck avoided an innocent person being shot: http://www.slate.com/articles/health_and_science/human_natur...
That's not very surprising. Many police officers only practice with their weapons once a year when it's time to qualify.
The average concealed carry permit holder shoots for fun, thus practices often.
Also, your second paragraph is somewhat ambiguous, I'm not sure if you mean to imply that the incident described is the only incidence of a confrontation with a deranged shooter. That is most definitely not the case. There are many examples of this happening:
http://www.denverpost.com/breakingnews/ci_20457445/2-die-sho...
http://en.wikipedia.org/wiki/Appalachian_School_of_Law_shoot...
http://en.wikipedia.org/wiki/2007_Colorado_YWAM_and_New_Life...
http://en.wikipedia.org/wiki/Pearl_High_School_shooting
http://articles.latimes.com/1992-01-01/local/me-1021_1_publi...
In any case, if we were to follow this argument further, we would expect that many more citizens would be armed, which would likely change things. Given the inherent confusion of such a situation, I would expect we would start seeing armed citizens accidentally shooting other armed citizens because they misread the situation.
Even trained, battle seasoned soldiers make mistakes.
Many people with guns feel empowered to double down in situations they would otherwise walk away from, and the involvement of a gun adds to the opportunities for a deadly outcome. Some gun advocates argue that an armed society is a polite society. I have my doubts about that, but I don't doubt that the consequences of impoliteness would be much more extreme.