Hi,
its more a definition of terms. He is correct Mach4 cannot control a machine, it requires a motion controller to do so.
A parallel port is a motion controller and as John has pointed out there is a parallel port version for Mach4. Its features are limited and will never be fully featured.
For this reason Mach4 essentially requires an external motion controller to be fully capable.
Mach3 it itself could not control a machine, it required a motion controller to do so, the parallel port being the best known. Mach3s parallel port is fully featured.
Notice the distinction between Mach and the motion controller. Most people considered Mach3 as one but is in fact two distinct pieces but running within the one CPU of the PC.
Craig