The pressure is the same all around the tire! that doesn't change. so how can it take less pressure at the top and more pressure in the bottom.

If that was the case, what is the sqaure inches of the whole tire and rim combined?  There is pressure on the rim as well as the tire so you have to figure the rim also. 

The tire pressure is not exactly the ground pressure but it is close.  The ground pressure will be a pound or two more than tire pressure.