In Phil's Chain Drive video he shows that the chain can be replaced without removing the swing arm and using an extended chain rivet tool to clear the M3W bodywork. The fact that you don't have to remove the swing arm to replace the chain, unlike the belt, is one of the chain drive selling points. I don't think that you will be replacing either chains or belts frequently, so it's not a big consideration. A chain life on the M3W is predicted to be at least 18,000 miles and there are many belt drives with over 30,000 miles on them.
