Having someone in charge of cutting the cake, handing out programs, being responsible for the guest book, etc. is a tradition at every Southern wedding I've attended (and I've been to many). It's the bride's way of letting her friends know that she wants them to share in her special day.
Not everyone can be a bridesmaid -- the cost would be too great. So this is a way for close friends to still be included in the ceremony and for people to know "hey, this attendant is a close friend/relative" even though the person may not be in a bridesmaid's dress or a groomsman's tuxedo.
Most of the time, the people who are asked to be cake cutters and things of that nature are just "honorary" attendants -- which means that they don't actually cut the cake. They just get to wear a nice corsage that lets folks know that the bride or groom singled them out as a special acquaintance.
