Yes do the diff and brakes. The early diff flush is to get rid of the clutch and metal junk during break in. This junk can foul the electric hyd pump and valves within the differential. As for the brake system they need flushing at least every 3 year. Just about every manufacturer now recommends it. Bosch, the brake manufacturer also insists on it, and they don't make a penny on a brake flush. A lot of little valves and moving parts in the modern electric powered brake system. Since brake fluid absorbs water from the air (you don't have a closed system, it's vented to atmosphere) corrosion will occur over time.