If you're a manufacturer that sells products, I'm not going to link to you no matter how good your content and how many bells and whistles you've got for promotions. However, if you don't sell products and you've got better content than I can provide on my site, I will link to you. I link to manufacturer sites when they have authoritative information that is beyond the scope of information I provide. For example, flame resistant clothing or fire rating information. If I want to cover my bases (ass) and make sure the customer has access to deep level information that is beyond the scope of what is necessary for a purchase I will link to it on a case by case basis.