Pat,
I think you bring up an interesting point. When I play competitive golf with a caddie, I am very reluctant to use a club caddie for a number of reasons. What I think you're underestimating here is the ability of these tour caddies to know the game of their player. Particularly when a player and caddie have had a professional relationship which has lasted a year or even more, there is an inherent level of trust on the part of the player that the caddie may know their game better than they do themselves, and an inherent level of trust on the part of the caddie that the player will not overreact to a major mistake on their part. It also depends on the type of caddie the player prefers. In my experience I find that club caddies tend to be "yes men" who are more inclined to let the player make his or her own mistakes rather than call them off, risking the chance that they could be wrong.
I'd like to bring up something that happened to me in the recent Philadelphia Open at Pine Valley. I should preface this by saying I had a legendary PV caddie who was on the money all day to this point. To avoid anyone going in the Devil's Asshole bunker, the GAP placed the pin on the 10th green all the way back, on top of that flat spot. I hit 8-iron in the morning from about 160 yards with a subtle tailwind. The ball traveled much further than I expected, pin high on the left edge of the green. We get to the 10th hole again in the afternoon and the wind felt to me like it was a little stronger. I said "let's hit the 9" and he said that the wind had changed and it was probably still an 8. Well, I hit 8-iron and it was so far over that it hit the tree over the green about halfway up on the fly. I think I could have gotten a PW all the way back. I ended up making double bogey and that was when I was really out of the tournament, moving to 7-over par on the day.The point of the story is not to say how terrible my caddie was at PV that day. In fact, he was great. It was my responsibility as a player to know my own game and trust myself to make the final call over him and hit the 9. The point is that if I had been able to have a friend who knew my game more than he knew the course, he likely would have been okay with the 9 over the 8.
What was worse about that incident than the double bogey was that even though he had been right all day prior to that, my ability to trust him went completely out the window. I was not mad at my caddie for telling me to hit an 8 instead of a 9 because it was ultimately my decision. But it certainly made it difficult on the next hole when he said "I think it's a 6-iron" from a yardage which I would usually hit 7 to actually believe him. Every shot I played the rest of the day was played with a question mark in my mind as I was standing over the ball. LPGA and PGA players trust their caddies inherently because they have been conditioned to through months and even years of a continued relationship. I think that is something you can't overlook when you claim that the player who "takes a Sebonack caddie" will win the championship. These ladies will likely be able to play Sebonack as many times as they want as soon as they qualify for the championship, and I'm sure most if not all of them will take club caddies when they do so. These ladies will have extensive local knowledge by the time they are ready to tee it up for a major on Thursday.