This is a relevant read: <a href="http://blog.priceonomics.com/post/50096804256/why-is-science-behind-a-paywall" rel="nofollow">http://blog.priceonomics.com/post/50096804256/why-is-science...</a>
The policy is imperfect, though, due to an opt out clause. <a href="http://www.michaeleisen.org/blog/?p=1413" rel="nofollow">http://www.michaeleisen.org/blog/?p=1413</a>