"After learning that some items purchased on eBay may have been used in the tragedy at Virginia Tech in April 2007, we felt that revisiting our policies was not only necessary, but the right thing to do."
Translation: "How many victims? And their families each have a lawyer. F&*#, that's a lotta lawsuits! We'd better be seen doing something proactive before they get the idea to come after us, too." The only "right thing" they are concerned with here is the kind that can be deposited in the bank.
Trust me, they've already crunched the numbers and have determined that firearms parts and reloading supplies net them only a tiny fraction of the revenue of, say, counterfeit Hello Kitty merchandise...
Who this is really going to affect is folks with old guns looking for repair parts. Maybe even more than Numrich, eBay was the place to go to look for that hand you needed for an Iver Johnson revolver or an extractor for a Frommer Stop.