The rim weights are probably the most important weights since they are at the outside of the circle. Cycling plus in the UK deconstructs the wheels and quotes rim weights separately. In my opinion, factory wheels should show the weights of the components. I expect that the rim weights of the two you compared are similar. You could easily drop the weight of a Mavic cxp-33 wheelset by choosing lighter hubs. I'm sure Ultegra would be a great choice.