stats and graphs are interesting to look at, just look at the earning list for 2012 ATP
It seems clear that most jrs. that do not go or complete (graduate) college will fail on tour.
Johnson (has not graduated, but attended for 4 years) and Klahn are two guys that have clearly established themselves to have future large earning capacity on tour (may be a few more, just using these guys as examples). May be a few others.
Now look at others (about the same age or school class - 0 to 6 years apart ) who either did not go to shool or left faily early......
Kosikowski, Mihdawy, McClune, Britton, Bangoura, Berman, Cox, Halebian----
i does not appear they can make a living on tour.
I guess the point is, go to school to get a degree or at least a good start on a degree, because making it on tour is tough.