It was a choice for pollution reasons from what i read at the time they launched their 3 valves/cylinders engines but they are to c.ome back to 4 valves from what we can read (the new V6 of the SLK has 4 v/c) and maybe big n/a engines for the AMG products ( i read 6.3 V8 for 500 bhp ..) . Wait and see
But will they continue adding the compressor as well in their powerful and sporty models?......I hope so, if not, its going to be a shame and a big mistake for me.