It's not so much that as the scouting reports were good but not great. Some prospects bust (Smoak) and some greatly exceed expectations regardless of their MiLB numbers. Are Hosmer or JMontero going to be the high upside player that some predict or will it be a good but not great prospect like Freeman, Alonso, Ike, Rizzo, Belt or a different top 100 prospect.
Sure you can never know for sure. But there are flaws with the process in general and the same types of players bust constantly. The no walk, no power contact guys, the really high K guys, the high K SP with no control of secondary pitches. The toolsy guys who don't do anything above average. When you see the same type of skillset fail at the majors over and over and over again you would think they would stop rating them so high.