Why do we need academic journals in the first place?

It may not get as much attention as the disruption that is occurring in newspapers, e-books or other parts of the mainstream media industry, but there is a revolution of sorts going on in the academic publishing business. It has recently exploded into public view with the boycott of Elsevier — one of the largest publishers of academic journals — over legislation that would block researchers from sharing their work. And for some, it has raised a broader question about academic publishing: namely, in an era of democratized distribution of information, why do we need expensive paywalled journals in the first place?