[zuprau]

Seems logical, but as a user, I can already choose the size of the content of the screen, I don't want you to choose it for me. So we all agreed that "16px text" is ok and we started designing the world around that.

As a practical example: my iPhone lets me chose between "native" and "scaled up" sizing. This affects the whole OS including the browser. Where does your "cm" measurement fit in that? Do you want to override my (user) choice?

Additionally, every browser lets me scale the content up and down between 50% and 200%, so "cm" is broken once more.

"pixels" haven't been "pixels" for a very long time, and that's ok, they're now just a logical unit.