Howdy
Rugers do not have a removable bushing, but they most certainly have a raised bushing, or gas collar, or what ever you want to call it. In the center of this photo is an 'original model' Vaquero cylinder, on the left is an Uberti Cattleman cylinder and on the right is a Colt 2nd Gen cylinder.
This photo shows the bushings pulled out of the Uberti Cattleman cylinder on the left and the Colt cylinder on the right.
The value of a raised bushing like this is to shield the underlying cylinder pin from fouling blasted out of the barrel/cylinder gap. The major cause of binding when shooting cartridges loaded with Black Powder. I can tell you that all three bushings do a great job of this when shooting cartridges loaded with Black Powder. For normal smokeless powder cartridges it does not really matter.
Getting back to your original question, yes at some point Colt began putting removable bushings back in the 3rd Gen, and some folks incorrectly call that a 4th Gen.
I have several 2nd Gen Colts, I do not own any 3rd Gens. But I have shot those that belong to a friend. I can see some tiny differences in the quality of the machining of the 3rd Gen vs the 2nd Gen, but not enough to make a big deal about. For a while, quality of the 3rd Gens was not the greatest, but Colt cleaned up their act. From what I have seen, the quality of the current crop of 3rd Gens, if you can manage to find one, is just fine.