There really is a fifth major element to the Internet Marketing Universe that we might call Big Sites.
Websites such as Amazon.com, the big weather, news and sports sites, and others, don’t depend on Search, YouTube, Social or Mobile. People know the sites and have them bookmarked or use mobile apps to reach them. So these sites DRIVE traffic to other sites in significant quantities.
They are especially relevant for websites selling consumer products or related to what is called “trending” topics – what is hot in the news. If that is the territory you are in, they can’t be ignored as they have the potential of driving a huge amount of traffic to your site – or deep sixing it.