The p2p architecture of bitcoin uses the redundancy very well for availability. It is enough that only few among the thousands of copies are online to make the system fully available 24/7.
If the usenet servers fall and I want my message - I have to ask around who has a copy. Who made a backup of my usenet post. That's less likely to work.

The bitcoin user MUST have a copy of the blockchain just to make transactions. No one makes you keep offline usenet archive backups ...
Once you have read the usenet post, you don't keep it, but the blockchain you do keep.

Any bitcoin block chain copies are present also on each smartphone with a wallet ... and that's where personal computation is heading. There will be no copies of the usenet posts on your phone, I assume.

Government order to delete a message from the usenet would probably work, but deleting the message from the blockchain wouldn't.

And the cherry is the cryptographically signed timestamp, that you don't have in the usenet. It would be very handy to prove prior art in court for example.

But we can all choose where to put our data.

BTCmsg,
at your service.