The search engines employ advance algoriths and technologies that are in constant state of evolution and innovation. Though the systems are brilliant, they require that the sites they index cooperate. Failure to maintain a mutual relationship between the site and search engine will lead to decrease in traffic.
Results in positions 1, 2, and 3 receive much more traffic than results down the page, and considerably more than results on deeper pages. The fact that so much attention goes to so few listings means that there will always be a financial incentive for search engine rankings. No matter how search may change in the future, websites and businesses will compete with one another for this attention, and for the user traffic and brand visibility it provides. One study shows that 56% of clicks and a third of time spent searching will be spend on the first link. 
Google represents 65% of the searches. That share is, more or less, stable. Bing maintains the other third of the market.
Many things that are in Google’s ranking algorithm correlate very well with brands. Google’s algorithmic inputs have started favoring things that brands are better at. Google is rewarding better links rather than just more links. They’re things around user and usage data.
The Latest Research:
A recent study shows that three key drivers of Google search rank are
Domain-Level Link Features – based on link/citation metrics such as quality of links, trust
Page-Level Link Features – PageRank, trust metrics, quantity of linking root domains, links
Page-Level Keyword & Content-Based Features – content relevance scoring, on-page optimization of keyword usage, topic-modeling algorithm scores on content, content quality/relevance
The following are least influential
Domain-Level Keyword Usage – Exact-match keyword domains, partial-keyword match
Domain-Level Keyword-Agnostic Features – Domain name length, TLD extension
Page-Level Social Metrics – Quantity/quality of tweeted links, Facebook shares, Google +1s
 F Takes – Leiden University, 2011 http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.228.4588&rep=rep1&type=pdf