FWIW: I know absolute nothing first, second or even third-hand about what actually went on at Apple then, but having once been in charge of developing and manufacturing an electronic product, I do know the following:
Apple is unusual, almost unique in that the company produces both software and the hardware it runs on. In a situation like that, development proceeds along parallel lines in various divisions based on general "orders from above". SO…
1) Execs poll R&D for new latest and greatest
2) Consult Marketing as to best ideas
3) Decide what to do and issue impossible-to-meet target dates
4) Scramble like chickens to pull the thousand different pieces of the puzzle together and actually have a new product to deliver.
Now when this all gets wound up and moving along, a thousand or so factors come into play: design errors, parts availabilities, Chinese supplier political issues, competitors product announcements, sudden new info from corporate espionage, unexpected failures/issues during testing and on and on.
In the FW aspect, if I'm an engineering manager in charge of laying out the board and they tell me "Don't worry, FW800 won't happen until the next model", if I'm smart, I know that the only certainty in the biz is that nothing will go as planned - therefore, if I can, I allow for FW800 if at all possible without compromising my timeline. That way, if things change, when things change, instead of having to tell Execs "Sorry, there's no more room for that, you said it wasn't needed" and having to look for a new job shortly afterward, I can just be the hero who saw the future and said, "sure, no problem…we not only left room for that, but it's already in the layout, just in case…What? a bonus? Oh really, I was just doing my job after all, but thank you.".
Or maybe, the supplier who swore they could deliver the FW800 chip on time didn't - simple as that.
These are obviously only two of a hundred possible scenarios, but you get the idea, I'm sure.
