Actually, it's the way it always been. Some improvements follow lessons learned from other models, and some follow supply. For example, when the DGT came out, 513's started to show up with the coatings removed from the string contact points on the bridges and the machines like the DGT. Tuners have been pretty much following the rest of fleet.
I think the uncoated tuners were introduced first in the ME I and then gradually moved to the rest of the line up...