Most companies recognize that socially responsible activities improve their image among customers, stockholders, the financial community, and other relevant publics. Ethical and socially responsible practices are simply good business, resulting not only in favorable image, but ultimately in increased sales.
"Ethical and socially responsible practices are simply good business, resulting not only in favorable image, but ultimately in increased sales."
That's exactly the point. It is not a selfless good deed, but just another transaction. Spend 20 million (not a huge amount for an ad campaign) get some good PR.
I am not saying that it is evil, shady or even questionable. But it should not be perceived in the same way as an individual donating a part of their income.
An individual donating probably means that they value some other things than money. A corporation donating means that they want "favorable image and ultimately increased sales".
http://en.wikipedia.org/wiki/Societal_marketing