It's probably a way to ensure the smallest incarnations don't bleed together. If bars also had vanishing points, the smallest incarnation would be defined by the narrowest part of the bar, this way the width of the bar is the unit.
One thing that also plagued my Compiz logo is that horizontally asymmetric designs can look like they're about to tip over. The new Windows logo definitely feels like leaning towards left to me. I tried to solve it by adding the third dimension, but I think the answer is more vertical asymmetry.. A real perspective.
