Well, you're neglecting that income inequality leads to political instability. While corporations may be benefitting greatly in the short term by exacerbating income inequality, it ultimately leads to an environment where it is more difficult to achieve financial success. I'm reminded of the story (possibly posted on talk politics?) of the inequality gap between Saddam Hussein's supporters and the iraqi populace being much greater than the income gap between the affluent and poor in european countries - it turned out that where the gap was smaller, the affluent made significantly more money than where the gap was greatest.

Perhaps I wouldn't call this a responsibility, though. I think it is more of an imperative to maintain stable markets in order to maximize financial outcomes.