It didn't break her spine.
Improvements where made to the Iowa class ships.
The 650 pound (comp. B?) warhead of a Mark 48 torpedo could break the spine of an Iowa class BB if it detonated immediately below the keel but I don't think "would is the right term.
As you noted the WW II torpedo hit the armor, modern torpedoes are designed not to hit the armor but explode under the ship and use the ships own weight to sink them.
Modern ship architecture has more or less abandoned armor in favor of electronic countermeasures and counter munitions.