Thank you, @smooth, for clarifying that for me. I suspected as much.
So, checking my understanding:

• Everything ever "Posted" goes on the blockchain.
• Every subsequent edit goes on the blockchain.
• The entire history of a post is accessible to an appropriately crafted UI.
• The "final presented state" of a post depends on the UI interpreting the blockchain history.

Does that sound about right? Thanks for helping me understand. ;)