for a long time, circuits like IASCA and USACi rated power classes as combined total power of amplifiers as per manufacturer rated power @ 4 ohms.
thus an Orion 225HCCA is rated as a 50 watt amp (25x2) when in reality it's half-ohm stable, and can produce up to 400 watts. Since the average amp is only 2 ohm stable, this gave users of the high current amps an unfair advantage in power classes if SPL was a factor in scores.
USAC is just trying to level the playing field finally to eliminate unfair power class ratings. In all honesty, I feel they should judge power classes on actual power based on either current draw, or amplifier load, but these are both difficult to measure accurately, and leave much room for cheating by dishonest competitors.