By this definition that seems to elude to cheating, couldn't any form of technology then be considered a "supplement"? Using online diet logs like fitday -- supplement; using this forum to get advice -- supplement; reading academic journals of the work of other people -- supplement; heart rate monitor -- supplement; chalk, weight belt, gloves, straps, and any other weight lifting accessory -- supplement; food scale -- supplement; athletic shoes -- supplement.
It's a matter of semantics, really, but ultimately just about anything can be considered a supplement. Whether you're on gear or not (I'm not), there's nothing natural about this sport. We're using a different shapes/forms of weighted resistance tools and moving them in various ways with our body, while manipulating macro and micronutrients, to create muscle tissue according to personal and social views of what looks appealing.
Not everyone bodybuilds/strength trains for this reason, but as far as true bodybuilding goes that's what it's all about. There is nothing natural about that. The human body isn't designed to be 230 lbs of shredded muscle. That's very counterproductive to survival, as it raises the metabolic demands (i.e. in times of famine the muscular dude will die sooner).
There is "cheating" and then there's using science to conveniently group the macro/micronutrients, amino acids, etc, that we need to put our body in the ideal state to achieve our dream physique.