Not surprisingly, given the readership of the Wall St. Journal, the reaction was to blame liberal bias for the decline.
But the claims that bias -- liberal or otherwise -- is the reason that newspaper quality has declined is a canard. Newspapers in most other countries have a political slant towards one side or the other. In fact, newspapers throughout US had often been politicized...until the theory of needing to be balanced came to play in the 20th Century. Just look at The Waterbury (CT) Republican-American or Rochester (NY) Democrat and Chronicle.
And claims that newspaper quality has declined has clearly been around since Mark Twain, judging from his quote cited in one of the letters:
"Mark Twain's observation that a 'man who doesn't read the newspapers is uninformed; a man who does read the newspapers is misinformed.'"(And let's not forget the newspaper report that famously and falsely claimed Twain had died before his time.)
I do agree that trying for balance has weakened journalism sometimes -- articles contain the "other side" of the issue even when there's not much of a case to be made for that side. I've seen that on issues involving both liberals and conservative perspective.
On the other hand, the trends that Mr. Kann cites regarding the decline of the quality of journalism (not just of newspapers) seems to be reasoned and accurate. And I find it interesting that he didn't blame liberal bias.
Perhaps, given that we live in a still-polarized country, politicized journalism is the way to maintain, even boost, ratings. That's a lesson to be drawn from the rise of Fox News and MSNBC. But that leads to an interesting point that Mr. Kann made -- the negative impact this will have on democracy. Relying on search engines, people will be able to select the news and the political bias they feel most comfortable with, and will be able to avoid getting news from "the other side." This will reinforce, not force readers to question their beliefs, which will serve to continue to polarize the country.