'Upgrading' to skinny tyres pointless for London commuting

This is Michelins thinking with the new Pro Optimum.

They're 25c training tyres with soft/light front and relatively hard rear (still only about 250g I think). Michelin say they should wear at the same rate as each other.

But wouldn't it be cheaper to run a Pro Race on the front and a Lithion or something on the rear, with little difference in performance between that and the Pro Optimum combo?