Why the need for more pins in processor? Why couldn't M2 just use the same pin configuration as previous processors?

DDR2 Memory controller may need fewe more pins.

Answer is easy, about half of them are used to deliver power/electrciity to a CPU.

Just some of the pins are used for techology or new features

So why does M2 use the same number of pins as existing Socket 940's, but aren't compatible?

AMD doesn't need more power for their cpus (~120W seems enough), but looks like they fitted DDR2 controller on same pins. There's no way for them to work on current boards, it's DDR2. Chipset + all circuits currently are build for DRR1

I heard that AMD was supposed to integrate PCI Express conroller or something similar on their cpus, that may change pin layout completely.