It is just out of curiosity ..

I think it's fair to say that at most top schools, most applicants will be rejected (UNC, Cornell etc). At mid-ranking schools (say Portland State University) it will be half and half. At no-name schools and for-profit schools, like Phoenix, I guess most students are admitted but a large number will not complete.

The US News online MBA rankings has some interesting statistics in this regard. Here are a few selectivity numbers:

IU Kelley - 76% acceptance rate
ASU Carey - 60% acceptance rate
Georgia State - 39% acceptance rate
Washington State - 51% acceptance rate

My theory is that the higher prices of the more reputable schools (Kelley, ASU) weed out a lot of low-quality candidates before they even have a chance to supply.

For reference, I think the selectivity rate in the IE Global MBA program is around 50%