You mentioned that they said they do charity work, siting the example of Katrina relief efforts.
That may be so, and good for them, but when JW's come to the rescue, they are there to help JW's first and foremost...if anyone else is aided, it is merely a collateral result. You can be sure they wouldn't help a DF'd person who's house was destroyed. Other organizations come to the aid of anyone in need. When JW's help non believers, it is often done with self serving interests in mind such as winning them over to their side or because of their never ending desire to make a good impression on the public regarding JW's and to legitimize their message somehow.