As far as I understand Artsofts reasoning, only the 25 pin PARRALLEL printer port is fast enough to provide the control signals to your machine, particularly when moving several axis simultaneously, to maintain the accuracy of what you are cutting. If you imagine a circle (or a sphere even moreso) all axis are continually moving but also continously changing speed, and a parrallel port is capable of doing this.
USB and other serial connectors have to convert the many bits of data into a stream of information, which all has to run at the same speed (by definition) and may miss the subtle timings of signals to your stepper drivers. Serial connections are OK I woud imagine for switches for limits, motor, coolant etc but not for the business end.
It may be that there is available a serial connection working at such a fast speed that these difficulties can be overcome, but I haven't seen any sign of it yet from Artsoft.
The printer port is only three addresses (suitably buffered) on the internal parrallel bus of the computer &H278,279,27A or &H378,379,37A the first address handling the 8 main data pins, the second address handling the 5 input pins and the third one the 4 other output pins, so as we know, you can get parrallel port cards to fit into your computer - yes - they are called second printer ports at the moment - maybe they will become just a parrallel port card in future, with perhaps say 16 inputs, 16 outputs - all addressable.
I dont know whether Artsoft will comment on this, but, yes, it would be nice to know, or obtain advice on which way to go.