Actually, an SWM installation is probably less dependent on solid copper. The problem is with voltage drop when feeding from a AT-9 or AU-9 dish. A 5 LNB dish draws enough current that the voltage drop between the receiver (which powers the LNBs) could drop the 18 volt switching signal down to where it might not be high enough for the internal multiswitch on the dish works correctly. With a SWM LNB, the PI supplies enough voltage that there is a greater margin. Since copper has less resistance than copper-clad steel, the drop would be less (Ohm's law, E=IR). The resistance of the cable is dependent on length, which is another factor and even RG59 might work in some instances, but Directv isn't going to take any chances with what they specify.