Microsoft has certainly expressed some interest in developing for the iPhone. (why wouldn't they?) Link
But I think it would be very difficult to edit Office docs on the iPhone, although presumably less difficult than on other mobile devices. I used to have a Handspring Visor with a mobile version of Office on it, and it was VERY tedious, but usable.
Ultimately, I can't see how Office can not be on the iPhone, but it may take a while.
I would agree that having document editing capability is essential. I was fairly good at editing/creating office documents on my Handspring Visor ages ago. One would not try to do extensive work on such a small device, but if you already have an excel document created and laid out, then the data input is simple, even on a small device.