Usually, paying somebody to do something that materially benefits you isn't called donating. As the article suggests, organizations should think of voluntary open source funding as insurance.

Of course, some companies do just donate money for open source, many more donate in kind - e.g. with hosting services - and still others develop internally and donate source code.

Naturally they do this because continued maintenance of the software supports their business objectives, and not out of an egalitarian sense of charity.