So what is its purpose? Should it give the author and audience a sense of belonging to the online world? Dissociating from people not belonging to the online world yet ("Neuland", anyone?). Just using it for teh lulz? Making things sound informal or less serious?
My experience is that I perceive articles preceded with 'Summary' instead of 'tl;dr' as much more no-bs-ty.
Edit: "Neuland" is referring to Ms. Merkel's "The internet is uncharted territory" comment by the way.