Body mechanics, leverage, and neuro-muscular connection definitely come into play. I could deadlift 430lbs for reps at my peak, and I while I was no string bean, I also didn't look all that muscular compared to the other lifters at my gym. I have ridiculously long arms relative to my height and relatively shorter legs, which gives me an advantage for deadlift. I had monstrous-looking guys watch me lift and then ask me what stack I was on. They didn't believe me when I said I was natural.