I may be off the mark but I believe when SVP holdings acquired Viking and Pfaff, along with the Singer name the quality of the Singer machines improved. If you look at certain Pfaff mid-range models and compare them side by side with the Singer mid-range to top of the line machines, you'll see some identical features, even machines. Singer even has one now with a built in walking foot.
In this day and age, the company isn't going to run 3 completely different assembly lines for all machines. There is bound to be crossover in features other than the top of the line machines. The great thing about it is that what is top of the line today on Pfaff and Viking will eventually be available on some Singer machines due to the trickle down effect.