Because AMD reference coolers are always well designed?
Non reference 290s now run cooler than most Nvidia gpus. AMD isn't Nvidia, they don't have a company that depends on the reference coolers (hello EVGA) and usually the only users of reference amd cards are OEM desktops, like Alienware. It changed with the 290/290x at launch but now anyone with common sense/not going watercooling doesn't buy reference 290/290xs.
I for one don't give a crap about power usage. If you're building a high end pc and care about your electricity bill, don't build something so high end. Besides AMD is usually cheaper so it'll take you a couple of years (atleast) to get any form of savings for going high end Nvidia over AMD.
AMD should have just paid Sapphire to design the cooler. Or even XFX or powercolor. Just not in house AMD, ok?