As I theorized earlier, they build such a quality product that even with stretched oil changes it can last through warranty. The new engines' use of alloys, twin-plug ignition, low friction cylynder liners, etc should make them cleaner than ever. Once your engine is through the warranty period it becomes YOUR problem not theirs. If you need a new motor shortly after your out of warranty they make more money. I"m not saying this IS what they were thinking, but their motives could be suspect. Also, as Benzmac said, the cost of maintenance can intimidate 1st time benz owners. In this era of lease programs, lux car cross-shopping, and owners who don't keep their cars forever the flexi-service makes more marketing sense. Not to be too pessimistic or paranoid, but MB is smart enough to figure out just how often you have to change the oil to keep the engine healthy just through warranty.
If you added up all the expenses of doing normal services (every 7500 miles) + "in between" oil changes (every 3750 or so) + the 15K services + the 30K mile services for 150K miles you would still have less out-of-pocket than your first major engine problem. Oil changes are the cheapest insurance towards engine longevity you can buy. If the cost of service is too steep then learn how to do your own "in-between" changes in your driveway. Most Auto parts stores take used oil free of charge. If there is sufficient demand we might even feature a DIY oil change article...
my pair of cents...Lee