One thing everyone seems to forget is availability of CPUs and innovation cycles. The x86 chips have very short innovation cycles and you can´t get the same kind of chip for more than a couple of years. A small platform however has to sell the same board for a much longer time to get back the costs of development. So unless you have the power to redesign your board every 2 years at least, you should probably choose a CPU that can be manufactured later in licence (ARM) or something that has longer cycles (maybe PPC).
If you continue on this thought, you will notice that drivers for other components suffer from the same problem, and that the main reason Linux is ahead of other alternative PC operating systems is that they get the drivers faster than anyone else.
