Since USB is a master / slave architecture, you'd need an active cable in addition to software and firmware to enable a USB master to act as a slave as you'd require for "Target Mode". If you just plugged two Master USB devices together with a passive cable, it would go horribly wrong unless they were specifically engineered to not follow the USB specifications.

Firewire is a very different intelligent bus system where any two devices can in theory talk to each other. It was designed that way.

We've had this discussion several times already!

And every time, I read it, think something along the lines of "that's interesting, I best remember that."...

Yup - FW allows network addresses, USB doesn't. So no Target Mode.