There are a number of reasons that the employment data does not tell the whole truth.
I heard recently, from a MBA student, that many students at business school go so as to not take greater risk in life, find a job, and get by...i believe that some would fit this description, perhaps most, but not all. So the schools that have less than 100 percent employment AND are considered great schools because they attract a "diverse" culture may actually be doing this. Some may leave school without the ambition of pursuing a "job" that counts as a job. Self employment would not be considered employment on these statistics. That being said, I would guess no more than 2 percent of a class that has taken on 100,000 dollars in debt would fit this category.
Then there are the waiters; those that have found employment but not accepted. these will be far more concentrated in the better schools.
Also, there will be those that get married and decide to live off of the other mba's income (I would not mind doing this)
International students may not show up.
This sort of brainstorming will lead to a lot of reasons a "diverse" class may not have 100 percent employment. The same can be made for starting salaries. Many interesting jobs do not pay the same amount as others. I try not to pay too much attention to this statistic. I focus on academic quality, student quality, life quality...anything that you can put quality behind (not quantity).