Real Green, you make a valid point in some manner. For instance, My son plays just down the street from where we live. Would my son have ended up there in the 80's maybe, probably.
I think PG makes it possible for those players who want to play farther away from home much easier for both the kid and coach (as BBallman said much better than I ever could).
A couple of the reasons my family choose not to send my son to a PG event was
1. He wanted to play within 3-4 hours of where we live. So we targeted events, whether it be showcases or tournaments he played in, that were in that area.
2. My son's ability as judged by others early in the process- He was deemed good enough to play college when he was a sophomore but not sure what level. Certainly not national at the time (or ever 
)
So for us, maybe showcases weren't necessary and he would have ended up exactly where he is. I guess the thought for us was he didn't know he wanted to end up there but could have been on of 50 colleges (those within 3-4 hours of home) when he was a sophomore and junior. A few showcases helped him be seen by almost everyone one of those colleges I would guess, plus others he never thought of.
Now that makes complete sense. If a kids target school is across the country than I can see how he would benefit from these services.
I guess for each is it about range from home and how to be seen. As said above, lots of ways to get there. PG and showcases are one.