Yes, it is to differentiate between new MacBook and MacBook Pro.
Moreover, IMHO, this is an indication that Firewire is dead within a few years.
Reading on this issue, I found some rumors that many notebook manufacturers will soon remove firewire ports from their products.
It's only rumors now, but having Intel actively pushing USB 3.0 (with CPU-usage and bandwidth-reservation issues addressed) and the disappearing of FW-enabled products (other than audio interfaces) let me believe this becoming be a reality soon.
Bad news: USB3 is not here yet.
Funny thing is that Apple itself killed the Firewire with its licensing terms.
P.S. I'd like to thank RME for releasing ExpressCard HDSP adapter. I think Multiface II was on of my most forward-looking purchases. As of now future looks good for PCI Express.
P.P.S. Even if FW will be removed from many notebooks I'm sure they will still have ExpressCard slot, where you may insert a FW controller. I know many do this already since not every internal FW controller is good for audio work.