Tyler PD80 power cables

I have the PD80s with the built in sub amps. The amps came with stock power cables which are 18/3. I can't understand why a 1000 watt power amp would be run with an 18 gauge cable and it just seems wrong. Would it make a difference if I replaced them with some cheap heavier gauge cables? I can't justify (afford) buying a pair of $1500 high end cables.

Thanks in advance for your opinions!