Until recently I ran my 1100 using LinuxCNC on a little Intel Atom box right from the parallel port—no Mesa card. It was connected to the Net, ran Dropbox, I’d open browser windows to look things up while running parts, not one hiccup in five years. The PathPilot UI is just another application that talks to the kernel, a browser window is no different and will have no more effect on motion control. Tormach won’t recommend it because providing support to the general public is costly and they can’t test every possible combination.
Also, I’m fairly sure some of the “real” controllers out there now do in fact allow you to access the web or run other applications on the control.