That is exactly what the article says.
> 00:04:51 GET /w/atom.xml, unconditional.
> Fulfilled with 200, 502 KB.
> [...]
> A 20 minute retry rate with unconditional requests is wasteful. [...]
And If-Modified-Since makes a request conditional. https://developer.mozilla.org/en-US/docs/Web/HTTP/Conditiona...
> Advised (via Retry-After header) to come back in one day since they are unwilling or unable to do conditional requests.
But I think it's still unarguable that the post doesn't explicitly mention If-Modified-Since, which it's not obliged to do, but the mention of it here could be helpful to someone. So why fuss?
If you're interested in it, I highly recommend just reading from start to end. It's all quite interesting (including building out a whole test service for feed readers to get scored on their behavior)