I'm sure Apple would have done the CDMA phone earlier if it weren't for the exclusivity agreement with ATT. The Verizon customer base is just too big to pass up.

This helps build additional loyalty for the platform and when LTE finally does come around, Apple will realize the repeat sales. Something that wouldn't be as easy with Android anyway, because there are so many companies competing with that platform, that it's very easy for one of them to get lost in any given product revision.