We have a few big plasma profiling machines on our site, and I used to work for one of the big companies, and I have never seen one yet with ballscrews on anything but the Z axis. All of the machines so far have railtrack and R&P for X axis, linear rail for Y axis and linear rail and ballscrew for Z.
Saying that we are just about to start work installing a 6KW laser with linear rail for all axis. Apparently this rather large lump of metal can hit 140 meters per minute on fast travel. For something that can profile 13mt x 3mt plates this will be interesting to see.