why are GPUs more powerful than CPUs

hmm more powerful you claim. they are not. the are designed for a single purpose, processing polygons. Now if you had a dedicated CPU for that you would not need a GPU if that make sense. Back with ISA was the standard the CPU processed everything the video card was just a interface to the screen, now we jump forward to PCI-X where you have 128bit wide bus , SLI, ETC and applications (games) with trillions of polygons to be processed so rather than have the CPU do it the video card itself has a CPU but we call it GPU, its own ram its on rendering built in with most cards to offload that job from the CPU to the video card itself.

Although it is true that GPU's can be more powerful than CPU's, it's not exactly apples-to-apples comparison. The clock rates are lower, the architectures are radically different, and the problems that they are trying to solve are almost completely unrelated. It is possible to harness the power for doing something other than graphics, but it's not quite mainstream yet.

I think it is because a CPU has more gates. While a GPU is solely for graphics. So some gates would be missing.

I'm not 100% sure though.

GPU's are highly threaded (generally running hundreds of threads) while a CPU may only run 1-6 threads (not counting hyper threading which only adds a small improvement)

GPU's are also more optimized for specific calculations (the kind done in 3d rendering)

With CUDA is becoming more popular, soon more companies will begin having their programs use both the CPU and GPU

Example of the power of the GPU

While it is good for many things, a GPU cant handle all of the same processing tasks that a CPU can and it is up to the programmers to properly divide the processing between the CPU and GPU in order to harness the strengths of both chips.

gpu has to do more complex calculations for graphics and another thing is that they take up alot more power and they are alot diffrent