Nothing to do with the frequency range, it's the DC their concerned with. They say the copper clad resistance is too high but who knows if this is a real issue or more of a CYA for longer runs. Personally I wouldn't like to put four runs of cable in only to find out that it didn't work, much rather charge extra for the cable and do it right.

One thing to note is that switching is no longer done by tones but by encoding.