Preventable injuries are the kind that start with a story line... like:
"Well, there were all these chainsaws sitting there..."
"I was pretty sure I could jump the 20ft to the next roof..."
"So I told him to drop the couch from the third story window..."
"I was pretty sure it wasn't hot anymore..."
"I didn't figure that a GI Joe could get stuck there..."
"So I'm blindfolded and I try to run..."
Everything else, the "I was just lifting like I always do and suddenly my shoulder hurt." stuff can't be prevented. All the prehab in the world while you feel "fine" is like taking tylenol because you might get a headache. Not that prehab is worthless, and there are some predictable times to use prehab. Big squatters should do some hip/knee prehab, as they are lifting weights that hold a higher potential for "acts of God." Likewise, big benchers would be smart to include some prehab for shoulders and elbows. Basketball players might be wise to pay a little extra attention to their ankles and so on. But otherwise prehab is a little like a preventative filling in a healthy tooth. Might help, but you never will really know.
I suppose if you have the time for it. Most people don't, or could use their time better in other ways.
Oh, and I'm not arguing with Eric, just voicing my own opinion on the matter for consideration by Ross and the general public at large.