To my knowledge, the actual limitation isn't the floppy drive itself. That is to say that a PC floppy drive could read or write 800 kB floppies.

BUT

Old Mac and PC floppy drives are nothing like USB floppy drives. The old devices were low level devices that needed a special controller to do a lot of the work for it (e.g. telling the motor that moves the drive head when to start and when to stop).

This means that the floppy drive controller is not the only piece of hardware that you have to consider. The other piece of hardware that you have to consider is the floppy drive controller. So even if a PC and Mac floppy drive were electrically compatible (which they are not), you still could not hook-up a Mac floppy drive to a PC floppy drive controller and expect it to read or write Mac floppy diskettes.