Chesterton's Fence states that you shouldn't make a change until you understand something's current state. Removing code because it's dead is folly, if you don't understand 1) why it's there, and 2) why nobody else removed it yet.
As this is a postmortem, it was proven dead code. There is nothing in the text that mentions that they didn't know what the code did (which then wouldn't be dead code).
