I don't understand the 250,000km / 15-year coolant change schedule for newer MB either. I would need to see what makes the coolant and components able to withstand the test of time. I know for example that 2000-2001 S500 cars in Canada already have rust. Many of the cars that came off of leases to the dealers had to be repainted, so imagine the cooling system.
The only thing I see so far that seems to be a step above is:
http://www.evanscooling.com/index2.html
Maybe giving them a call and asking them might help you get the answer you are looking for.