I wrote about that in my original post before editing it out. These kids could gain a lot off the court from a sophomore/junior season. Maturity, work ethic, etc. from staying in school could perhaps, lead to a longer and more successful NBA career than leaving as an immature freshman.
But that's a hard decision to make and a hard result to quantify. There are plenty of examples of 'hot' players whose stock fell after coming back to college.
This is something i've thought about a lot as a UK fan. Some of the one-and-dones from the past couple years have indicated they wished they were still at UK the year after going pro. The business and travel of the NBA is hard and I couldn't imaging having that responsibility as a 19 year old. I hate that kids feel they have to jump to the NBA but that's really how it has become.