alt Hacker News> It's the great irony of digital media. Copying data is accurate to the bit and is preserved "as-is", but in practice, it requires someone to maintain servers, to care about it. To separate out what is worth preserving.
This is a bit idealized. In practice copying data is not quite accurate (especially in bulk) and bit-rot is a very real phenomenon, both in flight and in storage.
You sometimes encounter it when dealing with files from the early '00s, it's very common to discover a few of them are corrupt, even if they've only ever been copied between harddrives.
Content-addressed storage and error correcting codes mean that one can make bitrot astronomically unlikely with honestly minimal infra investment.
It's copyright that causes anything to disappear from the web IMO -- torrents never die.
EDIT: I am aware that unseeded torrents do in fact die. But it really doesn't take much to seed a whole hard drive's worth of rarely requested data -- this also detects bitrot and so corrects errors automatically if you're not the only copy.
If you are, there's ECC, as well as making another copy.