ATI also throttles furmark, and has been doing so for longer than Nvidia. You make it seem like a one colored issue here.
Anyway, as long as the cards aren't throttling during actual use, and they aren't, it's really a non-issue.
Yeah, that!
If I recall correctly ATI started throttling furmark around the time of the 48xx cards, largely for the same reason Nvidia is doing it now: Furmark's obscenely 3d-like power consumption is a safety hazard.
On temp vs amps:
First a disclaimer, the specific numbers in this example are made up on the spot.
The effect and situation described is real.
Technically, it's always heat that causes the death. Always.
The thing is, if you exceed the maximum amount of amperage that a mosfet can deal with it suddenly goes from something like 99% efficient (only spewing out 1% of the power going through it as heat) to 90, 80, 50, or less.
So this poor little mosfet that is designed to switch 50 amps at 1.3 volts (65w going through it) is used to having to get rid of maybe .65w of heat. Not really that much, but enough that a tiny component should probably have a heatsink.
Now lets say that the absolute maximum amperage that this mosfet can sustain is 55a, that gives us a 10% safety margin, not bad at all.
Now some user finds the voltage slider and the OC slider and cranks it up to 1.4v, and due to that and the OCing this poor unfortunate mosfet is now switching 60a at 1.4v. There's 84w going through it now, but rather then putting out 1% of that (.84w, still not that much) efficiency has fallen through the floor and now it's putting out 30% as heat. That is 25 watts.
The component can't even get 25w to it's surface without overheating, let alone get it to the surface, through the TIM, and into the heatsink.
It quickly goes past it's ~125*c rated maximum temp, the hotter it gets the worse the efficiency gets, it's a positive feedback loop.
Like all positive feedback loops, it ends with destruction, eventually the mosfet looses it internally, and odds are it starts arcing inside.
So it goes POP! And then most likely it gives your GPU core 12v to think about.
Alternatively, your card may be designed such that in 3d loads, even nasty hardcore 3d loads, it's at 50a of 55a allowable, but furmark's math load puts it up to 56a. Pop!