Maybe there's not much to add, but I enjoy the topic :-)
Active Army officer 1981-2005. Assigned M1911A1 1983-90 (SN#1943589--great trigger & accurate!). M9 1996-98, 2001-02. All logistics units, not in combat. Personally, I liked both a lot, and have owned civilian versions of both. My military versions never jammed once in range use, nor did my two personally-owned M92FS. My privately-owned M1911A1 by Springfield Armory was a jam-o-matic, but likely due to something the previous owner did or perhaps something easily fixed, but I was stationed in Germany & had no way to get it sorted out.
Impressions:
1. Lots of .45s were seriously worn, although that was in large part a result of units not understanding how to get something done by Direct-Support maintenance. My unit learned the procedures, and got decent repair work done. Many in the military just don't know how to use the system, which can be slow & frustrating but it DOES work pretty well if you learn the paperwork. . . .If you don't, your stuff decays, whether pistols or tanks.
2. In the Ordnance & Artillery units I served with, about half the officers could hit targets with their .45, the rest were sorry with the pistol, OK with a rifle. No ammo was available for logistics enlisted soldiers to even shoot .45s, so they had no training with sidearms & weren't assigned them by tables of org/eqpt. In the Ordnance Officer Basic Course ('82), we fired about 2 mags for familiarization, whereas we qualified with M16A1. In OCS at Benning ('81), we never saw a sidearm--only rifles. (Mine was an XM16E1, no kidding.)
3. In log units with the M9, training with sidearms was equally abysmal. Target shooting once in a blue moon, and no good training available unless a self-taught pistol aficionado was in the unit. Recoil didn't scare shooters as much as the .45, but unfamiliarity was just a shame. Grip size too large for many.
4. My time in Germany was in nuclear ammo, serving on joint US-German warhead storage sites. We (US officers) carried .45s and had no prospects of resupply while in nuclear support of 2nd German Corps Artillery. Period. Wouldn't have gotten 5.56mm for our rifles either. As far as main-force logistics went, the idea of NATO units giving each other ammo was an absolute non-starter anyway. Any division or corps unable to obtain pistol ammo would have been so "broke" that pistol ammo would have been the least of its problems. I never learned this officially, but can only conclude that "ammo interchangeability" only mattered in strategic logistics, i.e. long-term war in which US might have been asked to supply bulk ammo to allied forces straight from our factories. . .but so little of ANY of our ammo types was truly interchangeable, it would make your head spin. I'm talking arty, mortars, rockets, mines, grenades, tank ammo, etc. NO WAY a German division would have ever gotten tactical ammo resupply from American ordnance ammo units, or vice versa.
How does all that translate to sidearm ammo selection? If it were so important, we never would have gotten NATO to adopt 7.62mm for rifle & MG, and then changed our own rifle to 5.56mm. I agree with others--no way that anybody is likely to care too much about sidearms at the macro level of procurement, and only special units train with them in worthwhile fashion. Sadly, for the rest of the Army, sidearms are primarily important only insofar as the danger exists of losing your career if they get lost or an accident happens. More effort expended on preventing those things than on training with the weapons. I'm sure that's SOMEWHAT different in Iraq, where sidearms are far more important than ever in NATO, WWII, Vietnam, etc. How much different now, I don't know.
Nonetheless, when s.o. needs a pistol, they indeed need it badly. Spec Ops units get some choice, regular units make do with what's available. I just hope that small-unit leaders in places where the troops really have to use sidearms for combat are resourced with time & ammo to train their people and/or let them practice. As poorly-trained as my units were with sidearms, the caliber or make/model were really the least of our problems.