Surely we wouldn't want to learn how to aim, huh?
Personally I'd rather not be stabbed to death or overpowered while assuming a decent firing position and carefully planting a glob of metal into an attacker's head.
I'd rather put all of my effort into not being killed, and putting a couple of rounds as needed in the right direction might be all I can do while fending someone off. I might find that I don't have time to aim carefully enough to neutralize the central nervous system, and that I have to settle for putting a few wound channels through my attacker to buy a little more time and a little more of his fighting ability.
Personally I'm not likely to worry too much about the capacity of a gun I'd be carrying, but at the same time, disparaging someone else's carry choice because they include rounds on deck as a part of the pros and cons is a little ridiculous. More shots is always going to be better than less shots, all else equal.
Everything isn't equal, and there is a point where you're sacrificing daily comfort or shooting ability or whatever, but that point certainly doesn't occur between five rounds in a carry gun and twelve or fifteen rounds in a very slightly larger carry gun.
Lots of very size efficient pistols carry 15 rounds in the magazine, it isn't like the Glock 19 or FNP-9M or CZ PCR are especially bulky or difficult guns to carry. You can't toss them in your sweats pocket, but not everybody has "comfort while dressed in nothing" as their primary concern when picking out a self defense gun. If you are dressed in 2012 presentable attire, not including skinny jeans, you can get a good holster and conceal any reasonably sized gun without much trouble.
It's just too easy to spend another $40-100 bucks on the other half of your carry setup and be really comfortable and happy with any of the myriad subcompact/compact/midsize guns available today to act like carrying more than a J frame is a sign of mental illness or lack of shooting ability.
I'd be a much more capable shooter with a Glock 19 or 26 sized auto than any of the pocket autos or small revolvers too. Carrying a gun that can hold more rounds doesn't mean you are carrying a less capable or less accurate gun. They're generally much easier to shoot well. The extra rounds are a function of size and design, not performance.