How was the 7970 a better choice? When every metric we looked at had the 680 winning at its release and then later tying/equaling the 7970 after the 7970's drivers took a course in awesome?
Specs in this case don't matter one bit. Even if the 7970 had a 512 or 1024 bit memory bus, if it still equaled the 680 with its 256 bus, then they're equal cards.
Now I grant you that the 7970 was usually a bit cheaper, so that's certainly important. But it is not nor was it ever completely superior to the 680.