Read both parts, it's good stuff.

I'm sure other data is out there, but I don't have it on hand.  But nearly everything I've read has indicated that there is definitely a positive correlation between high pitch counts, particularly over 120-125, and both short-term and long-term injuries as well as performance declines.  Correlation doesn't prove causation, no, but it's awfully hard to 'prove' injury causation with numbers.  Nevertheless, the data is there.

I agree that mechanics are the crux, but the reason pitch counts are important is that mechanics break down as a pitcher fatigues -- as he throws more pitches.  Throwing a high number of pitches in one inning can be more damaging than a 'high' total for the game, throwing high numbers of pitches in many games(particularly without ample rest in between) is particularly worrisome, and pitching in high-pressure/high-leverage situations may also increase injury risk, though that one's a bit sketchier.  

How about Mark Prior?  He supposedly has more or less perfect mechanics(can't say myself, I'm no scout), but he's had problems with injuries since being ridden hard by Dusty in the 2003 playoff push.  I can't prove that the overuse caused the injuries, no, but we can't prove that it didn't contribute to their occurrence either, and given what we're seeing about the correlation between riding a pitcher too hard and injuries, it seems likely that it had something to do with it.

For todays pitchers only Livan Hernandez seems able to hit high pitch counts consistently, but thats because he claims to pitch at 70% most of the game, and reaches back to regular levels under times of stress in the game. His mechanics are never altered by fatigue, which is what causes the injury, because he does not allow himself to tire out.