Yes, but they didn't require a large soutbridge and northbridge that x86 uses. For a discrete system on x86, you need a northbridge, soutbridge, CPU and GPU. There is no room!I think it is a lame excuse. The 12'' iBooks and PowerBooks contained discrete GPUs in an even smaller package all the time and offered battery live well ahead of the competetion during that time. It can be done.
The northbridge on the 15 inch is as big as the CPU and GPU chipset.
Here is an image to show you. http://www.ifixit.com/Teardown/MacBook-Pro-15-Inch-Unibody-Core-i5-Teardown/2212/2#s11319