People that rank on the Hare scale of psycopathy are over-represented (relative to prevalence in broader society) in corporate C-suites, controlling for age, gender, race, etc...[0] I am not sure what the representation of MBAs is in the C-suite but I assume it is also fairly high. I do not believe the book examines the representation amongst MBAs specifically, though.
There are several orders of magnitude less people in C-suite positions than in MBA programs. If most needles are found in haystacks, it doesn't mean that haystacks consist mostly of needles.
"Over-representation" is also pretty vague and the leap to anything like "common" is completely unjustified. A paper co-authored by Hare (referenced below) cites a prevalence of 1.2% for "potential psychopathy" (couldn't find a number for strong psychopathy). So if 2% of C-level execs were exhibited potential psychopathy, then psychopathy would be way over-represented, but still quite uncommon.
[0] http://www.amazon.com/Snakes-Suits-When-Psychopaths-Work/dp/...