Without clarification or context (i.e., "a new blockchain"), then it is usually Bitcoin.
"blockchain" or "a blockchain" to me is generic. "the blockchain" to me refers to the most famous one (Bitcoin)
How is this any better than a database?
Decentralized store and decentralized trust. The latter is hard with a publically accessible & editable mysql.
Except that this isn't decentralized - its a controlled blockchain that's only available for public download (which http does just fine) As does archive.org
I think you incorrectly understand how the blockchain can be updated.
It's not. This use case is pretty stupid since regulations make it impossible to allow true anonymous p2p trading.