I disagree. Someone found a bug in his essay and he removed it. No point repeating it to future visitors. In general, the final copy of a document does not include strikeouts.
I find that most good blogs tend to mark such after-the-fact revisions in a manner similar to that suggested above. Otherwise, there is no coherent article for the readership to discuss. There's the version you read, which is different from the version I read, which is different from the version Alice will read tomorrow...
I was actually not aware that there was an accepted finality to online writing though, so that is something I should keep in mind.