Frankly, FireWire 800 has established itself as basically a standard used by video pros for external storage. That's not the only thing it's useful for, but that's pretty much who's using it.
FW400 has a place for DV video, and Apple had BETTER keep including it on every single Mac they ship for the forseeable future. But FW 800 is (sadly) more or less a "pro" format now. As such, the 17" MBP, which is your portable editing studio, has it, and the PowerMac replacement probably will.
Everything else, no, and I can see why. They probably should have put it on the 15" MPB, but no way it's going to end up on an iMac.
It's a shame that FW didn't scale as quickly as it was intended, since at this point external SATA has pretty much taken its place for very high-speed external storage. Again, 400 is ingrained for DV video, but for high speed storage, 800 has already lost the fight for the most part.