It's perfectly reasonable to have separate drivers for different
hardware devices.  You don't need to smoosh them together just because
they have the same company logo on the box.

> On the other hand these two drivers would be the only ones in the whole
> system having the same manufacturer and the same bus architecture.

Actually, there is at least one other example: the Adaptec 1542
(`aha') and Adaptec 1522 (`aic'), which are both ISA SCSI controllers.
(Although this is a little different in that one is a `smart' board
and the other is a `dumb' board.)