as to why the iMac doesnt have a FW800 port,
that is a good question.
i dont think there's any real answer.. probably marketing.
maybe they dont want it to be too good, and usurp G5 + Powerbook sales.
anyway, yes, as you'd expect FW400 is about half the speed of FW800.
still ok for working with DV or HDV.
cheers,
nick