No, we don't forget about those drive caches. But in practice,
for nearly everyone, they don't actually matter.
The kernel can crash, and the drives, in practice, will still
flush their caches to media by themselves. Within a second or two.
Sure, there are cases where this might not happen (total power fail),
but those are quite rare for desktop users -- and especially for the
most common variety of desktop user: notebook users (whose machines
have built-in UPSs).