Nancy,
You are correct in guessing that it is a tradition. It is actually an old Scicilian tradition that was practiced mnay years ago in Sicily. A father would never refuse a "reasonable" request on his duaghters wedding day. If he did, I believe that it would spell bad luck for the marriage! Heck, maybe The Don's refusal to Kill for Bonasera turned into bad luck for Connie's marriage! Just an after thought on my part. Never actually looked at it that way before! Old Italian Superstition!

Don Cardi