All modern browsers zoom the document rather than scale the text, so pixels are now the best way go.

I've seen it persuasively argued that rems and ems with a pixel fallback is the best way to go.

http://csswizardry.com/2011/12/measuring-and-sizing-uis-2011...

Is there anyway to turn that off? To turn it back to just scaling the text rather than the whole document?

Why is zooming the whole document the preferred method? It feels sub-optimal to me, but maybe I'm missing something.

Hmm. Good point.

Although using px makes for an easier example, you don't have to mention the scale in which you are sizing your ems. The example was about the spacing, not about the unit used to determine the distance between heading and paragraph.