Hi, Motorep,
The .22 Long is definitely neither popular or common, though it is still made. There is a little problem firing shorts in a LR chamber, as you can get lead buildup in the area where the chamber stops, and this can prevent chambering of the LR. Takes a lot of shooting, but does cause a problem.
Back in the old days, a lot of guns would not feed the short or long very well, and most semi-autos would only function with LR. So makers were telling the public that this gun would work with all three and was more flexible. Besides, .22 LR was $.40 a box and .22 Short was $.23, so a gun that handled shorts was better. You could say the change in marking is a sign of a more prosperous society.
Jim
