Common People... or am I not getting that this thread is one big joke.
CPUs...
In order for a software to run on a platform it has to be compiled ("talk" in the machine language) of the platform.
Here are some platforms that are being used by consumer computers:
PowerPC (G3,G4,G5,etc... and even IBMs servers) - Platform with many advantages.
x86 / x64 Architectures (Intel Core2Duo, 386, 486, Pentium, AMDs, etc...) - The most common consumer PC platform.
ARM (Intel PXA, Samsung, TI OP)- Now this one is being used for portable devices...
Why ARM? - because it's energy efficient, it doesn't have a real-time hard clock (if I remember right) and its basically ultra portable so it's being used on most portable devices such as:
cell phones, PDAs, iPods and all of those.
Included with them are - Palm's Products, Blackjack, HTC, iPhone and most products we see portable.
Just like anything else in order for an Operating System to run on the product it must be written for it.
and in order for Input/Output (keypad/buttons, display, touch screen/pad, bluetooth, wifi) it must use specific drivers and firmware.
So basically the iPhone is just like most of HTC products except of the touch-screen apple introduced.
However, in order for one OS to run on the platform it must be designed for it.
Windows except of Windows Mobile / Windows CE based can't run on those machines without very nasty re-writing of the product.. (Vista/XP)
Apple however uses OS X which is NextStep. the main reason Apple bought NS was the portability of NextStep OS.
"Universal Binaries" and all the "magic" is within NextStep origin. so most if not all components of the OS can be ported (just like Linux... mmm... OS X is kinda linux... FreeBSD

).
The iPhone is one of the first commercial Linux (FreeBSD) phones out there.
Apple tries to hide the possibilities but OS X for mobile is one of the most powerful Mobile OSs being used today. (handicapped in Apple's way

)