I don't think this is a revelation or shocking. Just makes sense that the longer you can watch players play and grow, the better judgement you can make. Just out of highschool is the minumum and four years of college is the max. Its a catch 22 in a way. With a four year player you have a very good idea of what your going to have, but the major question then is, is what you see now, all that your going to get, or is there more growth left? Thing is though, your probably sure of where the floor is.
So how do you make a rational judgement on a player out of highschool. Well, if you saw Lebron play in highschool, he looked like a 26 year old man playing with a bunch of 8th graders. Except, they weren't 8th graders, they were what was left of the best highschoolers in the nation. The first time I saw him play, I didn't have a doubt that the was likely to be a very very good NBA player someday, it not a star. So in his case, it wasn't that hard. I'll say this, I think the competition in the top basketball highschools is far better today than it was 20 years ago, and if a player can dominate that competition, then its probably a fair bet your looking at a potential good NBA player.
By the way, some people have discarded some of the so called all star highschool games as not being truly competitive. In a few cases that's true, but in some, where it's the USA against the rest of the world, such as the under 16/17 games, the competition is quite good. When the competition becomes nationalistic, the fire starts to burn bright.