Those amounts I quoted are for people that graduated in 2002 meaning they started medical school in 1998. Cost of medical education (and the cost of living) rises each year and therefore the mean average debt for graduates will be higher for later years.
The best total breakdown I could find were for graduates in 1999:
Less than $50,000 - 20%
$50,000 - $99,999 - 40%
$100,000 - $150,000 - 26%
Greater than $150,000 - 14%
Obviously this continues to shift upwards (such that the 2002 figures i could find have 20% in the top bracket).