The previous example you have seems to deal in a more 'high level' driver. In that you're dealing with an abstraction layer already (talking through other low level devices and using a protocol).
Writing a device driver requires some pretty hefty usage of registers, IO addresses and interrupt control. Easy in C (well, sorta), but (as far as I know, and I'm far from a guru), a bit of a nightmare in Perl.
Also, a low level device driver is a real time system, and with all the best will in the world, I'd really break a heavy sweat if anyone asked me to code true real time systems in Perl. It's just not designed for the task.

Just my tuppence worth,

Malk