Almost all mercedes transmission until the last eight years or so have reccomended service at 30,000 miles, and if you do it properly, the trans will last an extraordinarily long time.
Overfilling is a big problem with the trans service, and one has to be very careful when refilling the trans to just put the fluid level between the marks and no higher.
As for service on the newer transes, the Mercedes Benz Club of America technical adviser suggests the same maintenance schedule as the older transes be performed on the new transes since it is basically the same trans that used to be in the old cars and although the trans is "sealed" it still has a filter that has no value unless it is changed regularly at 30,000 miles.
My take on the thing is that it is a marketing ploy by mercedes. Since everyone else's transmission needs no service for 100,000 miles then neither should theirs whether or not that interval would improve or extend the service life of the trans. "Service" now is to replace the trans at 100,000 miles when it goes bad, which is a very expensive way to maintain one's car.
You did the right thing by changing the fluid, but how did you determine the proper fill level without a dipstick? The only way that I know to do it on one of these is to carefully measure the amount of fluid removed and replace with the exact same amount. Overfilling will still lead to premature transmission failure.