Well, there is nothing natural about bodybuilding. It's not part of our human nature to be able to bench press 300lbs or squat 500lbs, or walk around with huge muscles. If it was we'd all look like Arnold without any effort. So it's kind of a strange thing to say some people are "natural bodybuilders".
Products like creatine aren't natural because if you stop taking it the body will return to it's natural state, and you will loose the advantage that creatine gave you.
Protein shakes are made from natural foods, but it is a processed food. Some people don't think processed foods are natural.
Natural to me is anything that doesn't interfere with the body's natural function or development.
Now here's the problem. Since bodybuilding is not a natural thing allowances must be made to allow people to reach gains that measure in the unnatural range. So products like protein shakes, creatine and others are allowed to increase the body's performance levels for functions that occur naturally. What we don't want to see is damage occuring. We also don't want to see people trying to change a body function to something it wasn't designed to do.
hehe
lol i did understand the point you were making though 
No nutritional supplements. Although, one could argue that cocaine and heroin (etc...) are grown naturally. These items could be considered herbal supplements. So we would have to define herbal supplements that perhaps are not chemically addictive to human beings. Then one could argue that caffeine is an addictive herbal supplement or any herb that elevates heart rate or blood pressure to a possible unsafe level. We could go a step further and say that any supplement that could an addiction or cause irreparable damage to internal or external organs should not be consumed by natural bodybuilders. 
