Because Mega-World Corporations have been ruled to be, legally, the same as a person (Corporate Personhood), they now claim that they have the constitutional right to lie.  They claim it is their right of free speech, as a person.  You can sue them for damages, and a court may find them guilty but they now claim to have the right to lie to consumers!

http://www.cracked.com/article_19485_5-outrageous-lies-companies-are-legally-allowed-to-tell-you.html