I was thinking today of the brilliant design of the D6 System with regards to attributes. I think it models actual human (and I would say, being) STR, et. al. rather well, rather realistically. It's not a linear system. Adding more D6 to a throw averages a higher number, but the curve flattens. The more dice you throw, the more likely a middle ground number will be achieved--and the less likely one of the extremes will be thrown.
The average of 2D is 7. Range of 2-12. 11 outcomes.
The average of 3D is 10. Range of 3-18. 16 outcomes.
The average of 4D is 14. Range of 4-24. 21 outcomes.
So, the jump between numbers isn't that large--not something that is hard to overcome. What's interesting is that the as the range gets longer, the most likely outcomes begin to bunch up in the middle. What I'm saying is that a character with 4D STR is more likely to roll 14, or a number somewhere around 14, than a character with 3D STR will roll its average of 10, or somewhere around that number. Less dice means more likely to roll the extremes.
Still, a whole die is a significant advantage, when rolling opposed stats. But, with say 3D vs 4D, it is easier for the 3D to roll an extreme of 14 or more. While, with the 4D, much bigger outcomes than 14 are quite possible, but there is more pressure to roll the average of 14.
And, thus, the weaker guy has a chance to defeat the much stronger guy.
I think that is brilliant game design.