By that standard all video cards are 'inefficient'. Efficient GPUs should experience little or no power loss. where do YOU draw the line?
Ultimately it's not a deal breaker for me if I have to pay for 300W extra with a pair of 480's over a pair of 5870's. Everyone's gonna have a different 'line' they draw where performance gain won't justify the price they're paying. Even if you earn just $12.50 an hour you could buy one of these in a week, and to pay for the extra power you'd have to work 2 hours more a MONTH.
I just want to be able to play the games I have and will have, do the work I do, etc.
To me, at the end of the day, if I'm running my games faster and they're looking better than yours and Photoshop is working faster, then I couldn't give two hoots if you come up to me and say 'well MY system is using less power'.
edit: btw, sorry if this post comes off a bit rough. I'm not trying to be a dick or anything and you make a good point.