The main difference between ball gowns and wedding dresses is that wedding dresses are a lot thicker, more layers, more structure, many have inbuilt corsets?
I saw some 1930s 40s 50s ball gowns the other day, from a time when posh women regularly dressed up in beautiful dresses. I wonder if that is the appeal of the whole expensive wedding dress and wedding thing to women today, why women dream of that before they have met the person they want to marry. If we had more posh formal parties with beautiful long dresses we'd not want to do the big wedding thing!