Re: BRIDE should be PRETTIER than the GROOM!
I’ve seen plenty of divorces where this scenario was present to know that this is an old wives tale.
But what makes you think it’s their “looks” that made the marriage successful? 
Perhaps those marriages are successful b/c the couples are compatible with one another, MUTUAL respect exists in the marriage, they have common goals for the future, and BOTH are willing to compromise in order to be happy.
Famous example if we’re considering looks only: Princess Diana was far better looking than Charles. That certainly didn’t stop her hubby from cheating on her…with a woman who wasn’t even close to what most would consider beautiful.