Scarbs says the Mercedes change is to move the wheels forward and the weight bias rearward. You can take this to the bank.
http://scarbsf1.wordpress.com/2010/04/2 ... edictions/
He says the 2009 Brawn was fast in part because it had ~49% front weight. This would have been a good match for the 2009 front slicks that were almost as wide as the rear and vertically stiffer than the rear.
Reading between the lines it appears the 2010 slicks have a more conventional distribution with grip and stiffness biased more to the rear tires.