To me, there's a big difference between high concentrations of natural substances and synthetic hormones, altered to maximize anabolic properties (i.e. steroids). To most people, consumption of the latter takes you out of the categories of "natural". As for the former, I see it like this:
Creatine is a natural substance, but I'm not trying to down a whole cow just to obtain the amount of creatine I get from loading CELL-TECH.
Whey protein, of which I consume at least 200 grams, comes from milk. Each fluid ounce of milk has one gram of protein. However, only a fifth of that protein is whey. So, to get 200 grams of whey from milk, I'd have to guzzle 1,000 fluid ounces (nearly EIGHT GALLONS) of moo juice per day. That ain't happening!!
That's my rule for buying supplements: Supplements are to provide nutrients, in extremely high doses, that are impossible/impractical to get from actual food. For this reason I believe many people deem people who use supplements, but not steroids, as "natural".