While the headline is nominally true, I don't thing this discussion is complete without talking about how browsers map this concept to actual device pixels ... particularly since they don't know how far the user's eyes are from the screen :)
Yes, particularly given that the spec explicitly says that for "lower-resolution devices" (i.e., normal computer monitors) the px unit should "refer to the whole number of device pixels that best approximates the reference pixel." So it turns out the px unit has quite a lot to do with screen pixels.
