I’m not quite sure exactly what to make of this but I found it interesting.
The ‘px’ unit in CSS is a non-linear angular measurement… The moon from Earth is about 24.3px wide, for example.
What it really comes down to is screen resolution. Discussions surrounding the pixel were a heated debate ‘back in the day’ but that was mostly due to an inability to zoom in IE. This puts a mathematical reason behind the choice to be less absolute in our CSS: screen resolution variance.
As Retina displays become more prominent, we’re going to be working with this circumstance all the more. Food for thought.