http://www.fangraphs.com/blogs/dusty-baker-is-throwing-caution-pitch-counts-to-the-wind/
Just playing devil's advocate for Dusty, 100 pitches is a completely arbitrary number, so who's to say 120-125 pitches is significantly worse?
The real research into pitcher's injuries needs to come with the stuff pitchers are now required to throw to be noticed by major league teams and to make it to the majors, which I hope outlets like Fangraphs are doing instead of spending so much time on pitch counts. Focusing on pitch counts as the number #1 way to prevent injuries is 1990's thinking. You can have pitchers who stay healthy, hold something back when they're starting and pitch to contact, or you can have pitchers who only have a 5-6 year shelf life and throw 95+ with wicked breaking pitches who strike out a batter per inning. At some point, you really can't have both, no matter if you limit starters to pitch counts of 100 or pitch counts of 120.
In that sense, I have a hard time criticizing Dusty that much for how he's using his pitchers. If modern starting pitchers are mostly 5-6 year assets regardless, why not have your starting pitcher pitch that extra inning instead of turning it over to a mediocre middle reliever? In a way, Dusty's usage might be smarter than a lot of other teams'.
Actually what the future probably looks like if major league teams continue to require pitchers to throw with lights out stuff is you have 3-4 inning starters, followed by 2-3 inning middle relievers, followed by 2-3 inning late relievers. Some team is going to figure out if you require your pitchers to throw 95+ with plus-plus breaking stuff, the only way to keep them healthy is to really limit their innings and possibly set up your pitching rotations like hockey lines . . . you have your ace pitching line of 3 pitchers for one game, your second line of 3 pitchers for the next game, and your third line of 3 pitchers and so on and so on.
What's really antiquated with the stuff pitchers are required to throw today is the 6-7 inning, 100 pitch, every 5th day starting pitcher, and sooner or later, some team is going to realize that and have a good sized competitive edge on everyone else. Until then, I have a hard time faulting a manager who thinks 120 pitches is the magic number instead of 100.