...but was he throwing 110+ pitches a game from the moment he entered the big leagues?
Precisely. Isn't Harang something like 30 years old?
There's overwhelming stathead evidence of a strong correlation between high pitch counts for young pitchers and subsequent arm trouble. By the time they're in their late 20s, pitchers' arms are mature and they can go much deeper into games, but it's depressingly easy to think of enormously promising guys who were overworked at 21-23 years old, blew out their arms, and were never the same. Mark Fidrych, Dwight Gooden, Steve Avery, Kerry Wood, Mark Prior, etc. etc. etc. Felix Hernandez's arm is already faltering; Seattle needs to be really careful with him.
It didn't seem to happen as much a couple of decades ago, which I'm sure is why Dusty Baker's attitude towards young pitchers -- man up and get out there -- is what it is. I've read a dozen hypotheses as to why that might be the case, but the two that make the most sense to me are:
1. Young pitchers' arms may have been stronger in the 50s, 60s, and 70s because kids played baseball almost year-round back then; instead of playing football and basketball in the fall and winter, they were still throwing a baseball. More work = stronger arms, and fewer injuries.
2. Much of the attrition had already happened by the time young pitchers got to the major leagues. Young pitchers whose arms couldn't handle the workload just didn't make the majors; many of them just got a "dead arm" (as they called it then) and went to do something else for a living. The relatively few guys whose young arms could handle the strain ended up in the big leagues.
I don't know whether either of these explanations are true, but any manager who sends Mark Prior out there to throw 120 pitches in a game is flying in the face of all the modern evidence. Homer Bailey might want to start asking around for recommendations of a good surgeon.