I love a tired out headline! But I have discovered why newspapers are dying, although I don't have robust timeline data and this may not be why readership is declining (but really if you can access it online easier...).
I was reading Lessig's Remix, and he says how newspapers generally get 1/3 of their income from classifieds, and how the market for classifieds has been decimated by Craig's List (ok ok, craigslist). I don't know of many businesses that can withstand losing 1/3 of their income.
Then I also saw this piece in Salon, about the firing of Dan Froomkin from the Washington Post, which was a pretty good explainer about the death of newspapers.
Note that newspapers are not the same thing as journalism. The people who work for newspapers may or may not practice journalism, but the two are not the same thing. Newspapers can suffer financially but that doesn't mean that journalism is dying.