You're right about the spectrum allocations, but given the way things are going, that might not last. First, the spectrum allocations were originally driven by

You're right about the spectrum allocations, but given the way things are going, that might not last. First, the spectrum allocations were originally driven by the need to deliver video signals that were compatible with analog TVs. Now that TV's are going digital, this might change the requirement for the traditional frequency split for upstream/downstream. There is no "physical" reason why you couldn't have a 400Mhz upstream range that matches a 400Mhz downstream frequency range. There isn't anything special about coax. It's just RF in a constrained medium.