As an industry, our position on what makes a quality link has changed over the years, specifically in the past 18 months, and most tactics have followed suit. The culprit for shifting our paradigm has been the Panda and Penguin updates that have made valuable content and natural, quality link signals a necessity.
With this push towards the complete removal of manipulative practices, in addition to an increase in the correlation of social signals and rankings – and I say correlation, because that is what it is for now – SEOs are left with a smaller tool set of tactics that work to produce link signals that are beneficial to a site.
In short, the gap between the links that actually work to increase authority and what Google says works is closing. And, if updates continue on this track, those opting for quick and easy links are going to find themselves booted.