The only difference is that XMR devs failed to mention that these files were not changed at all. What parts are you talking about in your copyright? If youre using a whole file without any changes - say so. Whats the point in this little dirty trick?
It's not a dirty trick, it just saves us the hassle of having to change licensing as and when we do touch one of those files. It's the equivalent of having *no* license headers, but then in the LICENSE file specifying that parts of the project are copyright the CryptoNote Developers - are you then supposed to list which parts are yours, maybe have a log of every line changed? No, because "git blame" does that already. Similarly, if anyone wants to know which parts of a specific file in the codebase have been modified, they could use "git blame" to see.