the entire point of graceful degradation is accessibility and/or continued functionality, so I'm not sure I get your point. The application of semantic markup and having it available as something we can gracefully degrade to is very much progressive enhancement.

Though I think people focus on "feature detection" too much as something one has to actively apply. With web stacks it's something that just happens. Screen readers and braille readers shouldn't -- and mostly don't -- give a flying purple fish about your screen media style. It's not that we have any means of detecting that. It's that they just flat out don't do it.

The same can be said of JavaScript or Images. We don't "detect that they're blocked or not present", they just go missing so we have to plan for "what if they aren't available?"

Which is why you layer them with fallbacks. Layering things with fallbacks IS progressive enhancement and creates graceful degradation. Even if we're not actively creating feature detection.