I would guess most of those people are, as you said, simply showing off their favorite/coolest/most expensive guns.
I think you'd be wrong.
Why wouldn't one carry a $1500 (or more expensive) pistol daily? I don't buy guns just to take them out of the safe once a month, wipe them down and gaze at them for a few minutes before putting them back in the safe (okay, so maybe a do have a
couple pieces in that category) ...
I want
the best gun (for my money) that I know I can depend on if I have occasion to draw ... My most expensive guns are my carry guns (my "collectibles" are all pretty much all older revolvers that have cost under $600 or so). Holster wear on a Wilson? So what? No one buys a $3000 1911 just to keep it in the safe.
Full-size? Most of us shoot "full-sized" pistols (or revolvers) far, far better than compacts or sub-compacts. Not to mention the capacity issue.
A 5" 1911 is one of easiest pistols to conceal there is (as others have noted).
I find I carry a 1911 in the colder months, typically a Colt's LW Commander (I have just decided the Wiley Clapp special edition is my new favorite 1911) or a 5" Series 70. In the warmer months, a SIG P226/228/229 conceals easily.
Yeah, I'll keep the $350 Taurus PT-145 in the tacklebox or truck, the type I'm not gonna cry over if something happens to it, but the one gun I want on me is the one I trust the most, the one which I shoot the fastest and most accurately.