You obviously don't remember the GTX 480....
AMD's current gen cards aren't as energy efficient as nvidia's, but they're way more efficient that AMD's previous gen (and on a par with, if not better than, nvidia's previous gen). That means they can go quite a lot larger - even with less efficient GDDR5 cards - and still be within sensible power draw limits.
I'm not quite sure what this obsession with a few watts, or even a few hundred watts, is. You computer spends most of its time idle or off, at which point AMD and nvidia cards have exactly the same power draw, so it's irrelevant. At current energy prices it takes around a 70W difference at load to cost you 1p an hour in electricity. You probably use more electricity reheating a pizza than you do gaming for a week. It's such a pointless conversation.