The 1911 is still in common use as a SD/HD/Combat firearm. Some LEO's and Military types still use variants of the 1911. It continues to be upgraded as a service weapon to this date.
The colt SAA, while a great pistol with a long history throughout American conflicts has not been used commonly by American troops or law enforcement in many many many decades. I would imagine the last LEO agencies larger than a couple of guys stopped using it as their primary firearm sometime in the 20's or 30's at the very latest.
The AR-15 as an example, the basic design started as the AR-10 about 60 years ago. Throughout that time the AR-15 has evolved, been upgraded and continuously improved. The “Guts” remain pretty much the same but the gun perseveres. Sometimes an old product continues to evolve, sometimes like in the case of the Colt SAA a better mouse trap comes along or they run out of innovations.
I guess in my mind the cutoff between "Modern" and "Not Modern" are weapons still in common use amongst "professionals" and in common use for Home/Self Defense. The 1911 fits that bill, while some of you guys might have a Colt SAA I don't think it is your "go to gun" in the event a bad guy kicks in your door, or you are a LEO pulling someone over on a dark country road.
"....The swords of others will set you your limits".