The difference between USB 2.0 and Firewire 400 is debatable. The reality is that most devices on the market to work with USB 2.0. Now if USB 2.0 is not good enough for you, I really don't think Firewire 400 is going to do it for you. You'll need FW 800 that is on the pro model just like it's always been! It makes sense.
How about the fact that the MB is now thinner and smaller than the old one, yet more powerful. That's a big deal believe it or not. People pay insane premiums for size and weight.
Kan-O-Z
It is not debatable, FW is faster in real-world performance. Audio equipment, harddrives, and miniDV cameras. Those are not USB unfortunately.