Please excuse me nitpicking, but
- the "One Ball Rule" is not part of the genuine Rules of Golf, and
- it's not being used by WGT IMHO (though it almost looks the same).
In the real game, the only imperative is to finish a hole with the ball you put on the tee.(rule 15), with some exemptions (e.g. ball lost, unplayable ball, ball in GUR). Players may change balls and ball types at those exempt situations and between two holes ad libitum.
The "One Ball Rule" is a special CoC named in Appendix I part C of the rules book. Thus, it'S not part of standard play. It's being used as an extra in professional and major amateur competitions and it includes that a player receives a DQ once he runs out of "his" type of balls. Remember Tin Cup?
WGT would be in breach of the latter condition if they'd apply this special CoC, allowing continuation with the Starter ball.
Me thinks that the reason behind this action is named in the OP's demand,
jacktbaldwin: a player should be able to choose another ball from his bag
In fact, there has not been a single choice in the game until recently (Mulligan in practice rounds). No choice to select a spot to drop, no choice to declare an unplayable ball, severe cuts into a player's rights. So why should they allow us to choose a replacement ball?
MisterWGT talked about this subject in last year's video chat and he did not mention the rule. He rather talked about difficult choices which WGT would have to make for the players...