Correct to some extent, no the GSM model despite having the exact same model #, is not the same phone, its actually two separate units, the GSM has its CDMA portion Disabled (permanently and cannot be enabled in any way) - Yes verizon does not allow phones not purchased through them on their network, but the GSM version because it has CDMA disabled, you are unable to flash it to carriers like pageplus etc.
IF one is buying a phone outright, best bet as I mentioned in my other thread is to buy the Verizon at full price as its the most valuable....today it will allow you the option to jump onto verizon should you wish and in future resale, allows buyer to choose between the 3 major carriers rather than just GSM carriers. hope it helps