Beeing the designer a Visual way to create the layouts, it makes sence the values to be layout variant related...This means that if you add several layout variants to your project in the designer, and then select one, the views position and size changes according to that layout
This way, if you add 2 layouts, but only manipulate the "Base" one, The OS will use that as base for resizing and re-positioning in the other layout variants, if possible...All the designer defined values ARE dip!
Therefore, Relative values would be redundant! I think...