Itīs normal and I would assume they put a safety margin on it so that no one (americans) would sue their ass if they get ticketed, or involved in some kind of accident, by claiming the speedometer was showing the wrong (read lower) speed. So to be on the safe side they turn it up a few notches. At least thats what I think cause you know, outside the U.S u canīt get rich by slipping on a wet floor in a random store.. even if u would break your neck
But, the F30 does show a more correct speed than the E90, only ~4 kms off vs. 7-8 in the latter.