48% faster when writing. That would mean more tracks when recording.
Not necessarily. It is a bit like comparing apples and oranges (very nice both).
USB2 and Firewire work a little differently inside the computer. They use different amounts of CPU power and set different requirements on the computer. This will show up in different maximum number of channels and in different minimum latency (and these two numbers affect each other). Reading and writing to a hard disc uses these resources in the computer differently from how you interface with a sound card. So simply looking at the transfer speed of disc writes does not give any accurate figure on how many channels of sound the interface can carry. To make things even more multifaceted different computers handles things differently, some better some worse. So it all sort of depends.
To boil it down, in my limited experience, USB2 handles fewer channels of sound. Yes. But enough is enough. I rarely record with more than 12 microphones at the same time. Add 2 channels for listening and the total goes to 14. And on a good computer, USB2 handles this at 96kHz sample rate, 24 bit. Enough for me and probably for almost everyone on this forum. Probably not all though, and then the point does become valid.
On one of my really old computers, there is not even any USB2 and that one could barely handle four channels at 44.1k. Things does indeed change, and in this case to the better.
Gunnar