Ones genes define EVERYTHING, that said with enough hard work and decent food ANYONE can getbig and strong. If you have the genes to grow easily, but to put on fat also (like i do) you can diet it off, but just have to work a little harder. Also many people say that they don't have the appetite to eat like they should, well you can allways eat more smaller meals and use stuff like weight gain powders.
Most of the time people are just ignorant and too lazy, they want the drugs to do everything for them. I have many close friends that use or have used AAS and allmost none of them were happy with the results.
That's because they expected too much too fast and were not willing to "put in the time" and also did not want to sacrifice anything as in skip a weekend of partying or so on. Charles Glass said that: "you should get close to your natural limitations, before starting to use AAS and when you finally start to use them, you should take the least amount needed to get the job done." These days allmost NO ONE does that, guys get on the juice without ever squatting or after a year of training.
That quote was not word for word, but you got the idea (yes it was from a magazine MD). Then i know guys that want to use gear, but are so afraid about the sides that they use some weird OTC stuff or use doses so low that no one could grow on it. As far as Arnold and the legends, they did not use stuff like SLIN, IGF-1 etc, but were able to make insane gains, that is because they, putted in the time.
And to answer your question, guys that grew bigger naturally, usually grow bigger on gear too. I know it is hard to except, but not everyone is meant to be very big, (and i love it, ha ha haa)...
About the genes, Lance Armstrong was an exceptional athlete, yet he probably could not grow to the size of a pro BB in any case, he's genes are different than say Cutlers, but still he made a living of being an professional athlete.