Why do <shape> elements only support rotate and translate?

Why do shapes not support matrix or scale elements? Is this intentional? Is it an over sight? Is there a good reason for it?

shapes have been designed mainly for rigid body (physics) engine. Most of shapes are not even stored in the COLLADA document but calculated at load time by the physics engine.
Shapes are the result of bounding volume calculation, which bakes all transforms in the shape.