Look at Fermi - was the GTX470 massively faster and massively cheaper than the HD5870 which had been out for six months?? Nope??
Nvidia still probably sold bucketloads of them.
People still bought the GTX480 in decent numbers even though it was not massively faster than the HD5870,was six months late and cost massively more.
One of the reasons the 470 sold so well was that nVidia (probably due to all the fuss about the heat, etc. of the 480) massively underclocked them out the box - a large majority would go from 607MHz to 800MHz stable on the reference cooler (if you weren't bothered with the fan ramping up a little) with no voltage adjustment and if you were ballsy they ran pretty well at 900MHz with a slightly risky voltage bump which needless to say was a pretty big performance jump over stock and made them a lot more competitive against the 58xx cards.
Downside was the amount of VRAM 1.28GB quickly became irrelevant compared to the core performance in SLI - its quite likely otherwise I'd have skipped Kepler entirely and jumped to the 1070 from the pair of them I had otherwise.