Here's a few links on the subject:
http://www.stateline.org/live/ViewPa...ontentId=15809

http://www.changetheclimate.org/court/letter.php

I personally believe though that with tv it has a lot to do with their other sponsers. The commercials usually run in groups of three so it would be like a Coke commercial, pro-cannabis, then probably a tampon commercial. Can't loose Coke money for a cause ya know!