Hi, listernoble and welcome to the world of MB ownership and to the forum. Please take a moment to complete your online profile by clicking on user control panel and filling in your location and vehicle. That information can prove very useful.
Those are actually the heads of bolts, not nuts, MB is like some other German marques in that they use lug bolts. That said, if the car has seen lots of duty in colder, wetter climes then corrosion is more common. My car started life in NY and the stock lug bolts displayed some corrosion, nothing terribly dramatic.
If the look bothers you there are lots of online sources from which you can purchase replacements for a good price. Also, you don't mention the year (unless you meant the registration as the MY), but going back a bit more than a decade MB liked to use lug bolts that had a long shaft above the ball seat so that the bolt head would be flush with the wheel surface instead of deep-set. Those are known to have a potential to break off above the ball seat, so if that's your situation I personally would suggest you replace them with the modern design to eliminate the possibility of the shaft breaking off.
Again, welcome to the forum.
Take care and enjoy the ride,