'Cause it's not as smooth as a conventional slushbox and thus does not qualify for the 600, but only for the AMGs.
Stunning car. And well, for us car-nuts S55 would be better, but Merc announced earlier that now, the badge would not reflect the actual cubic inches but more the performances.
Thus the S400 Hybrid which is not a 400, but feels like one thanks to the additional electric engine... And this is why the turboed engines will get higher designation badges than N/As because they feel quicker.
Badging is now reflecting the performance level and how the motor feels, not any more the mere "size" of the engine. Which actually makes sense, because with the current downsizing trend, MB would have to replace almost every model with one with a lower badge, which would be a marketing suicidal nonsense.
BMW, sharing the size-designation with MB, came to the very same conclusion.