I'm not sure if I agree with your thesis here. Big brands use their connections, resources, cash to get their brand front and center on social media (& mass media obviously) and essentially buy their way into prominence. Companies use Facebook ads and the types of companies listed at http://www.buyfacebooklikesreviews.com to essentially try and buy their way to popularity. Regarding the #cokegooddeeds hashtag, for every negative comment you'll see attached to that, you'll see about 50 positive ones. Most people are subtly affected by those ads towards brands. These big brands aren't going for marketing where users take some specific action, but they're going for advertising where they saturate the planet with knowledge of their brand. In this context, I think brands do buy their way into social media for all intents and purposes.