In some large organizations, marketers and executives don't interact with consumers unless a specific complaint or issue happens to rise up through the system. This clearly provides a limited and skewed view.
Marketers would benefit from opening up channels for more regular feedback - good and bad. Learning how consumers use their products and what they like affords an opportunity to understand what is working and why. Additionally consumers will often surprise brands with descriptions of product usage that were either unknown or undervalued. As Starbucks learned, it wasn't 'just' about the coffee.
Negative comments of course help brands as well. The sooner a company is aware of an issue the quicker they can solve it.