The actual reason links to studies are often left off articles (particularly in cases like this with sharp deadline pressure to publish fast before the competition) is that the software powering the editing and publishing workflow really badly needs improvement. An incredible amount of work and knowledge goes into a story like this.
Versioning rich text through many different software tools designed for writing/editing and publishing across many platforms is hard. Sometimes people copy/paste by hand and in doing so a link can go missing. The news industry needs more technologists to work on these problems. We're hiring for people to do that, by the way: http://developers.nytimes.com/careers/
(Also, the link to the study is now in.)