Using belts for timing is a cost cutting measure that puts more margin in the sale price of the new car, and also serves as a gift to the dealers in the form of increased service business. When MB resorts to the use of timing belts, I will have purchased my last MB.
The failure of a timing chain is rarely the chain itself. It is more commonly a broken rail, failed tensioner or improper reassembly.
The key, especially for the V8's is to inspect the rails and associated components on a regular basis. If you replace a perfectly good chain, you are increasing your odds of failure because you are introducing the possibility of incorrect reassembly. Also, replacing the chain without paying attention to the associated components is probably a waste of time, and there again adds the risk of incorrect reassembly. One bolt left loose or pin not fully seated could prove disastrous whereas had it been left alone it may have lasted forever.
Your most valuable chain maintenance is FREQUENT oil changes, regardless of your choice of oil brand. Leaving the oil in too long builds up microscopic particulate that will wear your chain prematurely, not to mention other engine components.