~160HP from a 1.6l is a lot and superchargers are inefficient and wasteful of fuel especially when pottering around town.
I've got a ONE and average about 35mpg. My last car a Punto averaged about 38 and it was only a 1.25l engine. I'm therefore happy enough with the consumption.
Not sure I believe the story about an M3 getting better consumption than an S though? The combined fuel consumption for the M3 is only 23.7mpg for the M3 whereas for the S it's 33.6mpg.