I know what you're taking about...the difference between just looking well muscled, to looking totally cartoon like. Believe it or not, its not the drugs. Well, the drugs do play their role, of course! But it's more about the training and the time put into shaping their physique. And of course, at the pro level, it has to do with genetics. When I say genetics, I'm not only speaking of genetics for large muscle but a whole host of factors. The SHAPE of the muscle belly. A guy can have only a moderate amount of muscle, but it can look much bigger with round shape and good insertions. Joint size is another factor. A round muscle that connects to a small joint is going to look a lot crazier than the same muscle on someone with thick bones. WAIST SIZE plays a big role. This might kind of relate to joints. A small pelvis and tiny waist will make the lats tie in to create a more dramatic "V" shape. These guys look good long before they take their first shot of test. Also, there is the response to drugs. There are super responders out there...guys who don't need to use massive amounts of drugs to get a strong effect and as these guys do raise their doses they aren't as prone to side effects. The less a guy can take to make good progress, the longer their life will be in the sport. There are guys out there that try to out drug the ccompetition, and this might work for a short time, but bodybuilding is a long term game and within a few years, it's these guys that get burnt out and have health conditions that take them out. 

The truth is, most people do not have the genetics to become pro or look pro, but that doesn't mean anyone should hang it up. The sport of bodybuilding is learning to improve the physique. No matter what your structure looks like, your look can be improved. It's about learning to be critical about your own physique and seeing what needs to be improved. This is a sport of illusion, so if your waist isn't the smallest, you can create the illusion of a smaller waist with bigger quads and wider lats. If your shoulder structure is narrow, it can appear wider with bigger delts. Don't neglect your back. A lot of non-competitors don't focus enough on their back development...in large part, because they can't see it in the mirror. But a thick wide back plays a huge role in your thickness and is highly responsible for your V shape. Besides back, the areas I see neglected the most are hams and rear delts. Rear delts will give your back a nice, finished look from behind and a rounder, 3D look from the side. Hams give your leg thickness and complete a physique.