They are going from the assumption that the Lawful Commerce in Arms Act is unconstitutional and that New York has an exemption around it anyway.
http://biz.yahoo.com/law/051123/ffb8a0274cd1b20c12723eb88dec7cdf.html?.v=1
http://biz.yahoo.com/law/051123/ffb8a0274cd1b20c12723eb88dec7cdf.html?.v=1