i'm a big AMG fanatic, and have read many, many articles on them. AMG reps have stated (unless misquoted) that on their SL55, E55 and other 3.2L SC & 5.4L models, that they opt for the 5-speed auto because it is the strongest of their transmissions, and there is too much risk of clutch burn-out and other maintenance issues associated with having a manual in their setups.
It was also said (though hard to believe) that mercedes buyer-data shows greater demand for the auto-stick than for a manual transmission!
also from what i have read, it is reported that the same durable technology in the SLR mclaren auto is bred into even our little 3.2L AMG kompressors in our car!

it is likely our transmissions can handle much punishment and heat! (i hope!)

they do now offer a 7-speed auto which is supposed to be as-bulletproof if not more-bulletproof than before!

i have driven the 7-speed auto, and personally, i think it's still pretty cool!