mahakalaa
268
If I am not mistaken all the older models had it.
It was a policy decision along the way taken by the Meylan family to restrict it to certain models to make it more special.
The double hairspring is also a complex bit of kit. Presumably adjusting and regulation will also be time consuming.
The same step was taken in terms of the size of screws as the older models had several different sizes that required the Technician to change screw drivers each time. This was made uniform after the take over. As in number of different sized screws was brought down in the later movements.