Good, in that case, I stand corrected. My original write outs will be corrected. However, I still think that lower priced bodies will not be as capable, due to market differentiation according to price points, meaning, now that entry bodies can do ISO 12,800, it almost certainly the next iteration of better bodies of the same generation will do ISO more than 25,600. Thus, cheaper bodies will always be 'less capable', unless you are comparing to previous generation bodies, of which the argument becomes moot. It's just that we happened to be at the peak of the technological jump, that we see such high ISO numbers, so in all due course, my explanation of cheaper bodies' ISO performance remains valid. Thank you.
Actually, if you look closely at Nikon's traditional line up. The differentiation between models is not and has never been, ISO capability.
Eg. D100, D70, D50, D40. All in the same generation. All ISO capabilities (and sensors) are identical.
Eg. D200, D80, D60, D40x. All in the same generation. All ISO capabilities (and sensors) are identical.
Eg. D300s, D300, D90, D5000. All ISO capabilities (and sensors) are identical (except for D300, it is a slightly different sensor. ISO same though). Nikon got lazy here, and in the D3000, they just reused the sensor from D60/D40x
It is this misconception you have, that many others also have, that makes them think a D300s will have better ISO capability than a D90 or a D5000. Boy.. they are so wrong.
It is not a definite that all manufacturers will cripple their entry level cameras in ISO. There are so many other areas they can differentiate their product on. If you ever used a D300s and a D90, you will understand why and how they can still differentiate between models while they are using the same sensor with same IQ and same ISO performance. They differentiate in build, functions, compatibility with advanced accessories, controls and speed of operation. Not IQ or ISO capability. But you are partly right that some companies are starting to do so (like Sony). But not all brands are doing the same. Maybe it is the start of a new trend, since price competition is so strong, that brands just want to push out super cheap entry level cameras that they used sensors from the previous generation. But then again a company like Pentax will come out with the Kx to totally dispell that notion, and "spoil the market" with a high performing entry level camera, with colors to boot too. It is like chess.