ApexPC:
In your son's USGA "Rules of Golf" handbook, look at Appendix I, Part C, 1. c - One Ball Condition
You are misunderstanding what you read. The first "suspicion" is that it is an appendix :)
Here is what it says...
"IF it is desired to prohibit changing brands and models of golf balls during a stipulated round, the following condition is RECOMMENDED...
(i)One Ball Condition. During a stipulated round, the balls a player plays must be of the same brand and model as detailed by a single entry on the current list of Conforming Golf Balls"
The key word there is "IF". In other words, IF your Club, Group or Tourny wants to implement a one ball condition, then it recommends using a conforming ball.
Again, I dont know about PGA rules and i dont ever think a pro would use different balls within a round as their game is so fine tuned to a specific type of ball, it makes no sense. As a former member of USGA, I dont ever recall this ever being an issue. My son has been a part of the First Tee Program here at East Lake in Atlanta for a few years now, I will ask one of the golf pros this weekend. But I am pretty sure the rule is clear.
As far as WGT. It is clear that they dont adhere to a "one ball condition". I wouldnt have a problem if they did. But since they dont, then dont half-ass it. Put a players already purchased ball in play, instead of having them waste money with having one/two offs that they basicall cant use. Not only will it save the player money, it will make the golf experience more enjoyable since they wont have to transition from their preferred ball to a "rock" during a round.