If you can believe the numbers on this site:
then GSM is about 4 times the size of CDMA worldwide.
But I think that 270 million possible subscribers should be big enough to recover costs for the development of a CDMA phone. And as far as I know even with 4G they would need CDMA for those providers because CDMA would be their fall back strategy when 4G is not available.
And I think Apple shouldn't hand a walled...