Battery life FTW!
The original 3 iterations of the iPhone became a hit cuz of this. The iPod Touch was already there anyways! So, people weren't seeing anything new. But, the battery life made it stand out from the rest. When the other players came in to the fray with full-screen touch phones, they just couldn't match the battery life. Of course, the touch screen itself was a class apart, but then the battery life was just amazing
And given the fact how much I wish my HTC Desire S and other Droids gave more juice everyday, Moto have hit it spot on with their strategy of making battery life their USP.