Joe Alexander is an exception to a lot of rules - not a 'path' that many can go. My recollection: the kid played in Asia and then got to the US for two years of high school ball. He was getting no interest from D-1 colleges and therefore went to Hargrave Military Academy for a year of prep school in hopes of getting scholarship offers. During that year, his stock grew, and Pittsburgh obviously offered him. A a relative unknown.. intriguing guy with potentially a ton of upside, but was still behind a lot of kids...
Contrast that with Rodney Williams, who had been on the recruiting radar of many for years, and has played AAU and with the big boys for years. Alexander played in only 10 games and less than 40 minutes the entire season -- Rodney plays 13 minutes a game and could earn more if he was playing better.
The only 'path' to the NBA for Alexander was to make people learn about who he was, and it was going to take time. Even after his junior year at Pitt, it was hard to figure out who he really was. The Milwaukee Bucks, with the 8th pick, learned that indeed they didn't know who he was. 2+ years after being drafted, Joey is the highest-drafted player ever to not have this third-year option picked up in the NBA.
But, there are plenty of examples of non-bigs that improve greatly over their college years and become high NBA draft picks (Gophers example.. hmm.. Willie!)