I have NO idea if the figures shown are accurate but do recolect that when the 5850 appeared the tests (with,of couse, immature drivers) showed that it was not that much faster than the 'old' 4890.
So might be a similar situation here.
True, but look at the time scale differece between the launch of the 4890 and the 5850 compared to the GTX 285 and the 470.