I'll jump in here. It's been "busy" for me this week and somehow I missed this thread. I haven't caught up on reading all of the responses, but for what it's worth, here are my thoughts on carrying "extra" reloads / "extra" ammo / high-capacity handguns.
1) You cannot miss fast enough to win a fight. So no matter how many rounds are in your gun, on your belt, where ever, you must shoot them one at a time and get effective hits on target. Otherwise, you're just shooting to "feel good" and that will NEVER win a fight.
2) Extra magazines are important when carrying a pistol. A magazine is a mechanical device just like the rest of the gun. If your only magazine is in the pistol and it goes down, you go from a very effective semi-auto pistol to a cumbersome single shot. Not good. I know, I know, I posted a wise-crack tongue-in-cheek response in the "How many magazines do you carry?" thread. But when I'm carrying a pistol, I carry at least one extra ammo feeding device as insurance against mechanical failure. Second, extra magazines are a source of extra rounds that MIGHT (but most often not) be needed to "finish the fight".
3) When carrying a revolver, I'm far less concerned about mechanical failure of the "feeding device". I prefer to carry some extra rounds in either a speed loader, or my favorite, a speed strip. Usually when toting a revolver I only pack one extra reload. I avoid reliance on loose rounds in my pockets. Like my keys, they never seem to want to be found when really needed. Also, when training with my revolver, I practice getting one or two rounds into the cylinder and the gun back up and getting a round on the target just as much (or maybe more) than I practice full reloads. A revolver with one round in the cylinder is "loaded."
4) Consider carrying a second gun versus a plethora of magazines and/or ammo for your primary gun.
5) For a private citizen, when normal rule-of-law is in effect, an ammo loadout that compares to a soldier in combat just doesn't make a lot of sense. Maybe put some reconsideration into where you go and what you're doing and make a few adjustments? Just sayin'. It's much better to avoid a fight whenever possible. A handgun on your person is, at best, a last-ditch tool to save your own (or another's) life under extreme circumstances. Train with your gun as if your life depends upon it each and every day. Expect trouble at any point in time and in every place you go. And pray that your training and mindset never have to be tested in real life by a person who is bent upon removing your choice in the matter.
6) For private citizen in a non-rule-of-law circumstance, a soldier or a LEO (both expected to run TOWARDS the fight), the context of this discussion is completely different. They still cannot miss fast enough to win, so effective hits on target are still necessary. It's just that they face a VERY HIGH likelihood of facing a plethora of targets that must be dealt with. Therefore, the ability to finish a protracted fight with multiple targets dictates the need for a greater ammo loadout and makes a higher capacity gun much more desirable.
7) Anyone, with a little google-foo, can find exceptions to any circumstance / situation. So, my thoughts on this topic might not agree with yours. Fine. You do you and go about armed and supplied in a manner that makes you comfy. I have no argument against that.