Some people want to play a 8 foot wookie that can rip the arms of a droid if it loses at chess.
Cannot a human do the same?
I agree with you about the role play and the incarnation of the character; but precisely, the example you give, within the rules of EotE a human (or any other specie) can do it too. It is not a "wookie only" thing. Since mechanicaly there is no difference in strength between a human a wookie, why wouldn't a human be able to tear the droid apart? and if he can, then again, which are the differences between a wookie and a human?
Well, I would say wookies are taller, they have their body covered by fur and they communicate by producing annoying sounds…a yes and they are stronger than humans and can tear a droid apart (or similar). The only thing is that the last one is not anymore true within the game rules, in the sense it is not a diference anymore, since any other PC with the same brawn score should be able to do it.
It seems to me that the diferences between wookies and humans have thined. I agree with you, as you said, this is a rpg and not all aspects come reflected by game mechanics. Still, we cannot neglect that some do, like the strength of a wookie. I don't see then, why a wookie cannot have more brawn than a human, why he cannot rise his brawn above the maximum of 6? It is a bit decaf that all alien races are equal in characteristics.