I am also quite surprised that so many people got surprised.
According to my experience, for a young (normally 27-28, with 3 years previous experience) MBA grad in top b-schools, their average salary upon graduation might be a bit lower than overall average if they work for industry companies. But for the guys working in IB and MC, the average will be the same. Therefore, for a top MBA grad 27-28 years old, I would say the average number can be around 90K. 100K is above average but not a surprising figure.