It's silly to compare GPU tests like this with CPU 'stress tests'.

CPU is very complex with a number of different units and execution paths and a bunch of cache.. it is very difficult to really stress the CPU simultaneously.
GPU on the other hand (especially one like 4xxx series) is a whole bunch of math units, which can easily be synthetically activated to stress the entire GPU.

Obviously ATi know that in 'real world use' (even GPGPU) applications can't utilise their chip in this way.. hence they make a design decision to use lower-cost power circuitry to meet 'real world' power designs. OK oh well, that's their choice and if you're the 0.0001% of people who care about 'synthetic stress testing' then you should avoid ATi products!

You can kind of think of it like a car engine. It can run from 0-7000rpm. If you run your car engine at 7000rpm 24/7 it won't be very happy Car markers will tune the engine according to durability vs cost and make design decisions based on real world usage. But sure, go stress your car engine :P