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 whol

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.