Reflects the "eye of the beholder" bit. BA's is supposedly informed by input from multiple scouts, so theoretically might be a better consensus-view thermometer than Law, who is a one-man evaluation team. As Dave noted, other factor may be different weighting of the value of a few primo, superstar, top-30-in-game prospects versus depth of 50-150-in-baseball types. If Torres/Contreras/Almora are on the very top of our list, those guys aren't exactly superstar candidates.
In Law's case, he may have been "brutally honest" on Vogelbach and Szczur in years past. But I think he's somewhat over-the-top hyper gush on some of the current cub guys.
*He's huge on Torres. Saw him in batting practice before a Myrtle game, and loves him.
*He's the most positive Happ guy I've heard of.
*He was super-buzzed on Martinez, as Blue mentioned, kind of the opposite extreme from BA's Badler.