not necessarily shitty h/w: it depends whether its properties suit your app.
(even with discs you could end up with an RL02, which had no idea where its head was.)
if you want to rewrite blocks indefinitely, don't use WORM or FLASH.
WORMS are good for archival storage but you can't write even twice to a WORM block.
in fact, that's a reasonably good analogy: because worms
are `different' somewhat different strategies are used by a file system to
allocate blocks for instance.  (eg, the `next' pointer
in the current super block might point to an allocated
but blank one, and so on.)

it's certainly true that people often assume they can exchange
magnetic devices and flash in a casual way.
is 100,000 a big number?  it might be.
is 1,000,000 a big number?  it might not be.
i carry a USB flash device to hold information that's updated at most twice a day.
even 10,000 is a big number then.