I think getting into the technicalities of the semantics is really an attempt to redraw the line.
While technically true, anything besides food, air and water could be deemed unnatural, there is a common understanding among most that the terms "natty or not" are shorthand for whether or not someone has used steroids. Some, maybe most, expand that to also mean chemicals designed to produce superphysiological responses (RC's, diuretics, etc). Others expand it to include practices such as blood doping.
In the end though, most people are content with the idea that ingesting whey protein, creatine, herb extracts, etc, does not cross the line of what they think of as natty.
The important argument isn't really about what each of us defines as natty (that's a personal choice) but more about the repercussions of those who are the furthest away from natty, but claim to be natty, and the impact that they have on others who might either try to emulate them, buy the products that they sell, or just give up early because they aren't achieving the same results (because they aren't being told the whole story).