I dunno. I think more than that are NBA-ready, they just have some serious developing to do to be more than bench players. If you read the rest of the article, it briefly touches on how the one-year rule has helped, and throughout it's pretty clear everyone feels the one-year rule would have helped Young. I think the one-year rule really changes the projected trajectory for a lot of players. Over the last few years, I've noticed several players that were highly-rated, but not at the top of their high school class, shoot up and surpass a lot of guys that were higher ranked coming out of high school. Some guys dominate at one level, but not the next. Having to go to college for a single year helps clear some of that air.
Malik Hairston was considering going from the preps to pros. He was considered a lock as a first-rounder. He chose college, and he ended up staying four years. He was drafted mid/late second round. He'd arguably have had more chances in the NBA out of high school, simply because of potential. Teams will ALWAYS draft on potential. That's the point - generally, you want to draft the guys with the highest ceiling (but you have to balance that out with the odds of reaching the ceiling or a certain talent-level). Generally, the one-year rule forces players to develop a bit more while exposing players' weaknesses and strengths better than skipping college.