Steve, that's terrible news. I'm very glad to hear that you came thru it with only some bumps and bruises. Cars are expendable, people aren't.
There does seem to be a pattern with our cars, front end collisions, and only the passenger side air bag deploying. I wonder if the same pattern has been established over on the SLK website (since those cars have been around longer). If so, it may just warrant an investigation (and possible recall) before some "drivers" get seriously injured. (If there hasn't been any already).
To add insult to injury, You didn't happen to get "cited" for failure to control, did you?
It might not be a bad idea to go to your family Doctor for a check up. If for no other reason than insurance purposes. Just in case some "medical" problems pops up in the future, related to your injuries.
Good Luck.