In the old setup, both FW ports were on the same bus. Anything with a decent enough data-rate to warrant 800 would saturate the bus, so using the 400 at the same time would actually decrease overall efficiency. The pro field is certainly moving towards eSATA for everything but offload from the master in data centric workflows. Hell, I'm even seeing LTO-3A tape drives in flight cases on set more and more!
The lovely AJA IoHD, which connects over firewire is one such device that fully saturates the bus.
Hell, Apple kept the old 17 for the video hardcore, which is something in itself. Actually it did the same with a G4 in the dying days of OS9.