There is no indication of a declining rate of sales (at least not in the steam data and not for the last few months) for the 5xxx series in the DX11 segment. There is a decline of market share which is not the same.
Since more DX11 cards started to appear the 5800 series has been on a decline of DX11 market share and the 5700 series went on a decline shortly after their launch too.
I have mis-leaded you when I use 5xxx. What I really mean is 58xx/57xx. They are shrinking in terms of sales. I am not saying that are not selling, I am saying that they are not selling as fast as before april.
The chart starts at april, and assuming no many people get there hands on the chip at September, the average percentage change for 5800 is 2.34%/7=.334%. For 5700, it should be even better since it was out at october.
This is logical as we knew at the time there are almost no competitions except some IGPs from Intel. After the initial the 57xx and 58xx have competition within the Dx11 segment. Some are ATI's mobile chipsets, IGPs, and 56xx/55xx. It really doesn't take a rocket scientist to figure out that 58xx/57xx isn't selling as well as before April, and based on the grade 4 math above, the numbers do agree with that.
Combining 57xx/58xx they actually took 4.77% of the market in 6 months, that is a lot of sells. Do not forget they never really have a price adjustment, meaning that they are really milking from them. In 11 months time, they milked 6.53% out of the market in total with the 2 series. That is a lot of sales. However, the rate of sales isn't as strong as before.
The average rate of growth on the chart for 58xx is .207%, down from .344%, indicating a drop of sales. Now that isn't an indication of AMD losing share from the market though.
Another indication is the rate of growth of Dx11 video card is more or less constant, yet the rate of growth of 58xx is decreasing. The former number indicate that the need of Dx11 cards have not been saturated, yet the need of 58xx isn't as strong as before.
None of these indicate any relation between the sales of 460 and the sales of 58xx/57xx. Independently speak however, 460 appears to be doing very well, and this forum won't be surprised. 58xx/57xx is slowing down, which this forum is also not surprised. In fact, we expected it.
What is going to hurt AMD isn't 460, but 6xxx. I will not expect 6xxx will come as strong as 5xxx as they came in where their are no competition. However, what exactly will happen if 6xxx doesn't live up to expectation? We know it will sell well if it is twice as fast, and we know it won't sell well if it is a brick. However, the result won't be so extreme. What if the first 6xxx performs like the 5850, will it sell well? or will it simply take over the portion which belongs to 5850?
AMD don't die even if 6xxx are bricks. They can simply adjust the price of 5xxx and they will still be good for a while. The difference is, doing better than before, or not as good.