Not necessarily as the GPU is still limited in what it can do, even though it is becoming increasingly more general-purpose.

The improved and wider-reaching functionality afforded by these new GPU's is not really the reason for the lower CPU clock speeds. There are many reasons why the clocks are lower, for example:
- Power / heat issues and management thereof. As the clock rate increases we don't see a linear scaling of power and heat output, hence cooling and power consumption can soon (relatively speaking) go through the roof. Not so good on a console where longevity, efficiency and low-cost are key.
- Modern CPU's are capable of doing more work per 'tick' than previous generations. What might have taken 10-20 clock cycles previously can now be done in 4-6 cycles. As a result, a seemingly slower chip may significantly outperform what's seen as a faster chip.
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We are now in a multi-core/-processor/-threaded world and it is far more efficient to distribute work over multiple processing units (at lower clock speeds) than it is to try and increase the throughput of a single processing unit solution with increasingly higher clock rates. Intelligent architectures with modern hardware / software designs are just a couple of the things that make this happen.