Yeah, the first thing I thought when I started seeing all those % Delta salary statistics was, "Wow, that is meaningless and easily gamed."
Someone who works essentially for free for a non-profit making 2k a year who switches to consulting will see a 5,000 percent increase in salary post MBA.
Someone who works in India making 8k a year will see a 1,250 percent increase in salary if they simply move to a first world country and get a job. (which might explain why everyone in India wants a foreign MBA)
I prefer the absolute figures a lot more.