High Current Pro HCP-850 850W TX12V v2.3 / EPS12V v2.92 SLI Certified CrossFire Certified 80 PLUS GOLD Certified Modular Active PFC Power Supply $99.99 After $40.00 MIR

Can someone explain to me why I should buy a "high current" power supply with a lower wattage output rating, vs. a higher wattage "standard" supply. It seems like a bit of marketing to me? relabeling a 1200w as a 850w? the actual outputs seem very similar. My ohm's law might be a bit rusty but this is not making any sense. I have looked for some information on a few mfg sites but cant find anything. your thoughts?

my new build - 3570k / z77 sabertooth / 2x gtx-470 / CPU liquid cooling / 16gb DDR3 -2400 , and I plan to overclock...