There is no css being loaded on http://thin.npr.org, just the default browser styling for html elements.
Of course, depending on the reasons behind the existence of thin.npr.org in the first place, NPR could add something really simple that doesn't add more than a few bytes and make it look several orders of magnitude more palatable.
Screw the CSS, let the thin page stand as a thin page.
Because browsers that did that would be both breaking spec compliance and introducing vendor-specific rendering, two things that IE proved were very very bad.
It's just that a) they're really ugly, and b) the mobile ones are ironically not mobile optimized.
html {
font-size: 2em;
}
Then your site’s 28px default font size that worked just fine on every browser now becomes 48px on mobile and breaks everything.