My recollection is the battery life issues between GSM and CDMA were comparing bare phone functionality (operating and standby). People who have an iPhone are likely doing much more than just making calls and having it sit idle.
that my old cdma phone's battery life sucked... but it was just a phone. It was fine, until one of two things happened: I had to spend a long time on the phone, or I was out of the service area. Then you could practically watch the battery meter fall.