fsync and hardware write cache

Something to think about:

if you run PostgreSQL with fsync on, but you use the hardware write cache
on your disk drives, how likely are you to lose data? Obviously, this is a
fairly limited problem, as it only applies to power down (which you can
control) or power loss where the risks may be reduced but not eliminated
with a UPS.

Does it make sense to add a platform specific call that will flush a write
cache when fsync is enable?