This 2.9 number comes from "Millionaire Mind," published in 2000 with the data from 1990s. The same book states that 2% of millionaires were in the top 1% of the college classes and 90% graduated from college. Note the huge amount of grade inflation since the surveyed millionaires graduated (their average age was 54, so they would be in college on average in the 1960s) and a large increase in the percentage of students attending colleges. And a myriad of possible selection biases. It doesn't seem like a good argument that people with poor GPAs do better than people with high GPAs.
Exactly. How much money did those people start out with? If you're from a wealthy family and will work for the family business it doesn't matter what your GPA is.