Basic EMC question

I've been doing some reading about EMC and understand the push behind
it was to create a standard control system that isn't hardware
dependent. The big question: is the control board function
implemented in software on the PC? That would explain the big deal
about an operating system that can output commands in real time - I
understand that standard windows can't hack it and Unix,Windows NT
and Linux can. My other related question is this: Why is it so
important to have a non-proprietary control system? It seems you will
still need a separate outboard power supply and drivers that WILL be
proprietary for each servo/stepper installation. I don't get it. I'm
not being a smart ass, I'm just learning. If it could ALL be
implemented inside the PC including power supply for the drivers and
drivers themselves then it would make sense to me.

Eric