I think often the "rules" for weddings come from the fact many weddings are in religious settings. The church wedding I went to where the mother of the bride wore a Chanel style skirt suit (except the skirt was a bum skimming mini), stiletto heels and a spaghetti strap with no bra certainly drew a few intakes of breath - it didn't get much better when she disappeared after the service and reappeared at the reception in a virtually transparent gold sheath dress - still missing a bra.
My (self imposed) wedding rules are nothing white or lacy, smart, dresses to be knee length or below, no see through or opaque bits and not masses of flesh on show. Your job as a guest is to be smartly turned out, not the centre of attention.