Firewire and Firewire 800 are backwards compatible, with the correct cord.
As for saying its stupid to have both, lets see you try plugging in a DV-camera when they have a USB 1.1 port and a Firewire 400 port, If you even could import video through USB 1.1, it would be poor quality, choppy and wouldn't even look the same as it would have on your camera, thats why a lot of cameras use Firewire for transferring.
If you have both USB and Firewire, why not use both? Saves the fact that you don't have to use all your USB port or all your Firewire ports.
As for Firewire networking, I would assume a lot of people would be using Windows XP, unless your computer is quite old. However, if you are using a Mac, I am sure a FireWire network is possible from using 10.1.x or higher.
Plus, on a Mac, you can connect one Mac to another via Firewire and use one as 'Firewire Disk Mode', which basically allows you to use one Mac as an external hard drive, for back up or large data file transfer, faster then using standard Ethernet or using USB 1.1, if that would even work correctly.
I have heard a lot of people say that Firewire is much more of a stable connection the USB, because its more consistent, but I can't be certain about that.