I believe that you are all correct in your comments and Digs did take advice from a US lawyer on the subject who confirmed that the Explanatory Notes were being misconstrued by those who said that ALL centre fire firearms were now not 'Antique' regardless of age.
However it appears that there are US dealers and authorities who are reading it as above.
I really hope that your very powerful lobbying system can get this clarified ASAP as I don't wish to made an example of by some overzealous customs official or ill informed policeman.