I wonder if shifting the motor to the top of the table is a marketing ploy, just to make them different? The idea works, as I have done it on a couple of machines (and fitted a speed reducer on top as well!) but in this case there's no room for a reducer on top. Plus, as kgg pointed out, the speed control mounted on the bottom could be susceptible to being kicked/knocked.
Personally, I prefer the more "conventional" system, it also makes it easier for tinkering with.