Today's game and today's pitches are not the problem. Overuse and not giving the arm a chance to rest is one of the major problems for adolescent pitchers. Unfortunately, the problem created at a young age sometimes does not show up until the pitcher is in his 20s and playing professionally. Here is a blurb from Dr. James Andrews and the American Sports Medicine Institute. The entire article can be found here and its a good read:
http://www.asmi.org/research.php?page=research§ion=TJpositionstatement
EPIDEMIC
During the past few years there has been an “epidemic†rise in the number of professional pitchers requiring ulnar collateral ligament reconstruction ("Tommy John surgery"). This is like déjà vu, as a similar sharp rise was seen in adolescent pitchers near the turn of the century. These two rises are indeed connected; that is, today's pro pitcher in his 20’s was an adolescent pitcher a dozen years ago. Thus in many cases, the injury leading to Tommy John surgery in today's young pro pitchers actually began while they were adolescent amateurs. Observations by orthopaedic surgeons support this link, as the torn ulnar collateral ligament (UCL) in a pro pitcher usually looks like it has worn out over time.
RISK FACTORS FOR ADOLESCENT PITCHERS
Research has shown that the amount of competitive pitching and pitching while fatigued are strongly linked to injury. Other risk factors may include pitching on multiple teams, pitching year-round, playing catcher when not pitching poor pitching mechanics,and poor physical conditioning.