I feel like this is a more complex problem to solve than it seems at face value or the author implies, especially considering tablets of varying dpi.

CSS dpi media queries are unsupported in Safari mobile and desktop, so that increases the complexity significantly.

Beyond that, the fact is most web layout is still done in px or other non-fraction-of-the-width units, so it’s often a matter of the wider layout simply being broken at smaller widths, rather than just refusing the display.