Whose language is it anyway?

Here is another article on the issue of copyrights, this time regarding brand names and other copyrighted words.  Do companies deserve the criticism they receive from articles like this one?  Is this similar or different from companies like Monsanto who have been crtiticized for patenting organisms (genetic variants they develop and then make it impossible for farmers to grow their own seeds)?  In America, everyone uses the terms Kleenex, Band-Aid and Jello for what should officially be called facial tissues, adhesive bandages and gelatin desserts.  Other brands, however, must settle for the official terms.  When does common usage make a commercial brand name a common word which everyone should be able to use without penalty?  And what limits should be put on companies in terms of patenting a word which is already in common usage?  (Thanks to Petra for this link.)