For voice transmission, the slight amount of noise/capacitance/induction and all that junk that are picked up don't matter at all.
However, when it comes to 56K modems, it's a different story entirely because they are pushing the corners of the envelope. Remember that 56K is actually limited to 52K (or is it 53?) by the FCC because getting there requires more power than the lines can actually handle.
Sometimes it matters, sometimes it doesn't. These guys are having the problem - so maybe it matters for them.
