well i'd like to see the number of people who actually travel outside the US.
It's not just travel, but also resell value. CDMA phones are hard coded to the network they were built for. You can't even take phones between CDMA carriers.
But a gsm phone with it's removable sim means I could sell it on eBay to anyone, even someone out of the US and they can conceivably unlock it and put in any sim they want.