So it seems that now you're complaining that the 1070 is too powerful and you'd have been happier if they'd made it slower but cheaper? (So like the 1060?) The gap between the 1070 and 1080 isn't massive, so it makes sense the price isn't too different.
Stop and think for a second.
Let's say for the 1100 series, nV take the 1070, make it 5% more powerful, and release that as the 1170 for the same price (£400). They then make an 1175, which is a decent chunk faster than the 1070, but also £75 more expensive than the 1070 launch price (£475).
As a 1070 owner do you: a) suck it up and buy an 1175 or b) complain that whilst there are more cards in the 11xx series, the real upgrades for you are now more expensive than ever.
Because that's what's happened over the years. Yes there are now more cards in the range. We have a Titan, and a Ti than didn't exist in the 460,470,480 days.
But whereas the 460 was a powerful card for £240* (3rd top, remember, and it chewed through all the games of its time)... the 1060 is now the 4th top for £300. And the 1060 does *not* chew through the games of its time. It's pretty feeble, truth be told, even at 1080p. The 1070 is the real equivalent of the 460, and it's £400+.
So yeah. £240 to £400 in the space of a couple generations.
*Adjusted for inflation and VAT rise. Actual price £150-£200 in 2010.
e: Just to clarify why the 1070 is the equivalent of the 460, not the 1060:
GTX 460 = GF104 (470 and 480 are GF100).
GTX 1060 = GP106 (1070 is cut-down GP104).
The 1060 is nV's 3rd-tier chip, behind GP102, GP104. The 460 was the 2nd-tier chip, behind only the GF100.