Many a times you'll also see a skinny guy with small, ropy muscles outpower a big guy with big bulging muscles. It's all about how those muscles work and not necessarily how much muscle there is.
This last is so. But, as Matt Furey attests, regarding strength (and even physical form, depending on how exotic your view is) genetics is not much of a factor. It's about mind. (following on polaris' comment, here) Bruce Lee's regimen was about endurance and flexibility. His strength came from his mind. However, I think some of the things he was into, machines in particular, were far less functional.
polaris: if you recall Buddabing's thread, I don't lift weights. (I also breathe differently than the average body builder, which prevents tensed, bulk muscle.) My concern with protein is that I oxidise fast and am hungry, particularly when training, otherwise. Though a surplus isn't good as it eventually wears on the kidneys and other internal organs. Another difference is that instead of carbs for energy, of which only a relatively small amount per day can be utilised, I consume a fair bit of fat (generally uncooked) which, conversely, your body can (note) cleanly burn in tremendous quantities. Due to the types of fat I eat, the lack of carbs to turn it into white fat, I have this constantly replenishing supply of brown fat that is readily used, and that also has a far longer sustenance, than carbs.
shardian: yeah, though the regular weight exercises are very limited, and don't address flexibility. Now, girevoy (kettlebells) on the other hand, you should see what the qualification for instructor is on that. The exercises are dynamic...and kets go up to at least 88lbs, which only the senior mother ---smurfs--- can do.
Another thing, though, you have to remember that wrestling hasn't been real in America for decades and decades. Gama, he was a real wrestler. I mean, unless it was merely external from scuffing an stuff, how the ---fudgesicle--- do you bleed from your ears in wrestling?
And on Gama: he wrestled with a tree. This is a TRUE type of isometric. On the physical end, the key to power.