Heh. I wouldn't use that particular example, personally. Mike Patterson, who has been known to post on AikiWeb, would be a better source, IMO.
"Iron Shirt" is simply an offshoot of (and inextricably intertwined with) the ki/kokyu/qi/jin skills, when practiced correctly. For instance, someone practicing their Xingyi skills *correctly* will wind up with an iron-shirt without specifically training in "iron shirt".