Regarding CDMA outside USA, the Chinese carrier China Telecom uses CDMA, and has close to 100 million subscribers. South Korea uses CDMA exclusively. There are 46 million subscribers for South Korean mobile telecoms. If only 1% of these subscribers chooses to buy an iPhone, that's 1.4 million phones.
Conclusion: Apple has good reason to produce a CDMA version of the iPhone. The real question is, Why did Apple wait so long? Exclusive deal with AT&T is my guess.
Recognizing the limitation of CDMA when traveling to many foreign countries other than China and South Korea, Verizon has a Global Traveler program that can help Verizon customers who are infrequent travelers get equipment that will work in your overseas destination. Call (800) 711-8300 for more information. I think the Global Traveler service is free, and can route calls to your USA number over to the international phone.
The iFixit folks have an illustrated teardown of the iPhone for Verizon. Among the interesting details is the fact that the new phone uses a Qualcomm chip that can handle either GSM or CDMA.
http://www.ifixit.com/Teardown/iPhone-4-Verizon-Teardown/4693/1
I expect the new iPhone 5 coming this summer will work with either CDMA or GSM. This would reduce inventory headaches, and give customers the ability to switch to a different carrier. It's less likely that the new iPhone 5 will have the capability to communicate at 4G network speeds.