I agree that you should dress respectfully at a wedding, and maybe these people think they have? Some people have different ideas of what is acceptable to others. It sounds like they made an effort to look nice anyway!

FWIW I have been to a "bogan" wedding (my uncle's) and it takes the cake for the worst dressed people LOL! One lady wore trackies and moccasins , but it was a very casual wedding and everyone was happy, including the bride and groom and that's all that mattered .