There are merits to single stack magazines & the pistols that run them:
1) Pistol designs that are slimmer than pistols running the same caliber in a staggered mag.
2) Profiles of larger caliber guns no larger than smaller caliber ones.
3) Single stack mags are generally more reliable than staggered - especially in adverse conditions.
You are indicating the single stack magazine design is obsolite which is patently false. The above is but a few examples of why the single stack magazine and guns that run them still exist. The Sig Sauer P220 is a prime example of updated pistol technology taking advantage of the single stack mag design.
There are many designs that still use the single stack for reliability when volume is a secondary consideration.
I agree about the hits counting - however this is a product of training and not the type or model of firearm used.
The majority of handgun fights are close in and over within 3.5 seconds according to some statistics, which largely discredits the capacity arguement.
Your facts are lacking. The Glock 21 comes in at 1.27 inches in width. The classic single stack 1911 from Kimber's website indicates 1.28 inches. 8 rounds vs 13, you do the math. The SIG P220 measures a full 1.5 inches in width for a whopping 8 rounds on tap. Sounds like a significant reduction in size for that single stack mag, good thing the P220 takes advantage of single stack mags. In fact, the P226 measures the same(1.5") and it offers you 15 rounds. The standard size frame for Glock measures in at 1.18" and offers 15-17 rounds depending on calibre. On that note, the myth of "stopping power" with greater calibers is just that, a myth. The 45ACP round is over-rated. However, should you fall into that myth the Glock still comes out on top. A Glock 31 offers you a width of 1.18 inches and 15 rounds of .357 SIG which by ballistic data is superior to the 45ACP round.
I'm not sure where you come up with the belief that single stack mags are more reliable than double stack. I see that most who run 1911's run someone's after market mags, Chip McCormick or Wilson being the two major players. Aside from Norinco problems the next most common 1911 concern I see, read, and hear about are magazine related issues. I have yet to hear anyone complain about a bad Glock mag, aside from their stiff springs when loading. In fact, two buddies of mine had SIG P226 pistols and they never had a magazine issue either. Hold on, another buddy has a P220 in 9mm with a single stack mag and the only issue I know of is the base plate coming off when the mag landed on a concrete floor. I don't see any trends in favor of the single stack over double stack.
TDC