Remember what T'Pau warned Kirk? That he might be disturbed at what he was about to see, but it was Vulcan custom? Well, at that point, T'Pring hadn't yet made the challenge. So what was T'Pau referring to?
Would the fact that T'Pring was going to be issuing the challange be that big a secret? I mean she brought her boyfriend to the wedding. And I do wonder if the presence of the weapons and the weapons carriers is a standard part of the wedding if no challenge is anticipated.
Possibly. But given the Vulcans' adherence to tradition, I would think they would be a standard part of any wedding. After all, to prepare for the worst possible outcome is only logical. Think of how embarrassing it would be if the bride issued a challenge and there were no weapons available for the men to fight with?
Besides, if Spock is allowed to bring his friends, why can't T'Pring bring her (probably only) friend?