Not sure about recalibration, but FWIW, my E90 consistently indicated 10% over the real speed, my E70 seems to be more like 8% (sounds similar to yours). I can't believe that this is not a deliberate move by BMW. My thoughts are that they:

- Err on the side of caution, by indicating more than actual, people tend to drive more slowly
- Like the fact that their cars seem faster than they really are
- Just don't care

Anyway, you can always just subtract 8% in your head... keeps the mind sharp!