How Formal?

My daughter is planning a large December wedding. She and the bridesmaids will be in floor-length dresses, but she`s wanting the groom and groomsmen to wear suits. I`m "old school" and believe if the bridesmaids wear "formal" dresses, then the men should be in tuxedos. The tux rental actually should be cheaper than those who don`t have suits and shirts buying them. What do you say?