My point was that a coax cable is better suited for a wider range of frequencies than a regular phone line.
Also, for the conditions where those cables have to be used (in many places they are outdoors, covering relatively long distances and exposed to the elements) a good quality coaxial cable is more reliable than a standard phone pair.
Of course a 10Gbit cable is much better than a coax, but the distance is much smaller and the external conditions are more controlled (or they should be). But a 10Gbit cable is NOT a phone line.
You are grouping ADSL lines and Ethernet UTP cables together like they were the same thing. They are not. Try patching 4 phone lines together in a couple of RJ-45 connectors and see if you can even get 10 Mbit ethernet working properly... and I mean working properly... not just link and small ping packets. Try to copy a big file over and see what happens.
Even using CAT-5 cables the throughput will suck if you mess up with the pairs order. Trust me, I've seen it and it's ugly.