I have several USB Floppies and they dont take the B: Drive letter. In Vista they have removed this limitation. I was able to give the data drive of mine the letter A:\ this limit is only for XP and before Windows OS's.
Well i was using xp at the time. When i built my pc i didnt bother with an internal floppy. i only use it when i am working on someones pc that has no boot from cd option in the bios and or requires a boot disk to install the os.
No, it is reserved for any kind of floppy. Back in the day, hard drives were small and there weren't CD burners. It was useful to have 2 floppy drives to copy files from one disk to another.