There's a related oddity in Inkscape's rendering (and probably the standards), the fact that the border is drawn so that it overlaps the fill rather than surrounding it. To be honest, the idea of the stroke surrounding the fill (non-overlapping) makes a lot more intuitive sense to me, especially when you've got thick and/or translucent strokes like Juan's example.

So you mean that (for example) in a rectangle with width 20 and height 10, and stroke-width 10, then the fill should be 20x10, and the fill + border should be 40x30? I believe that saying that the shape specifies the center of the nib of the pen used to draw the stroke is intuitive and makes sense. To me the current resulting sizes are ok. The only thing that I don't like is the effect with translucent stroke.