This is not true. The shareholder value myth has been debunked by law professors.
"...shareholder primacy theory was first advanced by economists, not lawyers. This may explain why the idea that corporations should be managed to maximize shareholder value is based on factually mistaken claims about the law."
http://www.europeanfinancialreview.com/?p=6482
"Contrary to myth, the sale of Ben & Jerry’s to corporate giant Unilever wasn’t legally required."
http://www.ssireview.org/articles/entry/the_truth_about_ben_...