I think it was just evolution. Buyers wanted 3" guns and the Win Choke system was very popular. Kind of see the same thing with shotguns now a days. New camo patterns, "improved" gas systems etc. Just marketing but with some measured improvement. I honestly think that Winchester had no idea how popular the gun would be and invested in improvements to keep it selling well. The model 1200 was about 40% more and was the same gun as the 2200 just with vent ribs and walnut wood. Easy choice to make on a farmer's, working man's budget.
Darryl