For low-level consumer stuff i guess it works. I've been a competitor at DB Drag world finals a couple years(1999, 00, 01), so i get how to make a meter work. But someone who buys a 100$$ 1000 watt amp is going to be at a huge disadvantage to someone with an amp that actually does 1000+ watts. You know all amps aren't created equal. RMS is a formula, but the only numbers you have to work the formula off of is the published specs, which on many cheap amps are simply an outright lie.
If you take on of these cheeseball amps and try to run it at a lower impedance, you very well may fry it. But I've run good amps at half their rated impedence for a long time, and often it's fine. My DB Drag car had 8 crossifre CFA-1000d's all running at .5ohm, and they lasted 2 seasons with no problem.

Again, I'm not trying to bust anyones nuts....I'm just saying power classes heavily favor people who spend more on really good stuff.