CE 6.0 supports four processor architectures, ARM, MIPS, x86, and SH4 - Windows XP Embedded supports x86 and PC architecture hardware - since XP Embedded is based on the same unmodified Windows XP Pro binaries (but componentized) the same underlying hardware
and processor technologies must be used in your devices.
Processor support is just one of the areas that developers look at to determine the choice of operating system - operating system size can be another (300kb kernel build for CE 6.0, 40MB XPE min build size), power management, real-time support, driver support
etc...
- Mike