I do think it is more of an i4 thing, it was introduced at the same time that i4 related information was added to the handbook.Could be more of an i4 thing, as new owners are saying that Sport mode tends to keep the turbos spooled.
Out of interest I looked up the running in procedure for the A Class (and by extension the A45S). Mercedes say that only the Comfort or Eco drive modes should be used during the running in period. Definitely worth bearing in mind for those of us who have got / will be getting the Mercedes engine.