It's the simple rule of cell phones...why come out with the superphone (lulz) when you can release small features at a time that will make users want to keep upgrading.
In Apple's case most Verizon users wouldn't leave their great carrier for crappy AT&T service, so when the iPhone DOES come to Verizon they will likely add a few new features too to entice users who still are wary.
HTC has announced that they have "3 core user experiences" that people like. I'm sure one is touch only, and another is touch + physical keyboard....third I have no idea what they might mean lol. However I'm pretty torn now because I'm up for contract soon and it's between the Droid, the HTC Bravo, (if they ever annnnnnnnounce it, unless the Bravo is indeed the Nexus One), or waiting for the Verizon Nexus One.
I'm so wary to make a touchscreen only jump...but the keyboard on the Droid just is not impressive or tactile enough y'know?