A few points:
1) Getting a degree is pretty important, no matter what. For all the "millionaire dropouts" there are hundreds of good old fashioned working-at-mcdonalds dropouts.
2) It's not necessarily untrue, but the statistic itself has less to do with gpa than it does with personality type or situation. For instance, a lot of people with low gpas are either unchallenged/uninterested, working their way through school, busy doing "something else" instead of going to class, etc.
3) Of my group of friends in college, I easily had the lowest gpa, and I do make more than the rest of them. However, the friend with the 2nd lowest gpa probably has the _lowest_ paying job, and another friend with a very high gpa makes almost as much as I do.
So.. hmm.. .ok, I guess my conclusion is that there is no correlation between gpa and net worth. The good news to that is that just because you have a low gpa it doesn't mean you won't get a good job and be successful. The flip side, of course - is that just because you have a high gpa doesn't mean anything either.
PS: I interviewed a dozen college students a few months ago for a job... there were some people with 2.5 gpas who were very well qualified, but a couple people with 3.7-4.0s that had absolutely no business leaving college with their degree. I mean, they had no clue. That's a shame.