Rapid, I don't have a huge amount of info for you. What I can tell you is that APT is a representation of the internal geometry created by the CAM program. Most CAM directly processes APT or the internal geometry data structures when it shows you a simulation. This is why a lot of folks find g-code driven simulators useful--they find problems your CAM simulator won't.
There are generic post processors and other utilities out there that can process APT. I think Vericut will process APT, though not totally sure of that.
It's pretty cool to access the geometry directly on CAM that supports APT. Not really archaic, it is just incomplete compared to g-code because CAM only needs a subset of the g-code.