The WSJ runs an online column called "Best of the Web". Granted, it slants conservative (which again, I am not - but it does poke fun at various media outlets/stories) but have a look at his point on the lack of coverage by the NYT on the issues facing the current Obama Administration: http://online.wsj.com/article/SB1000142405297020448830457443...
I don't know if investigative journalism has declined independently. What I do think however is that there is far more investigative journalism happening outside of traditional media outlets which has made traditional media outlets considerably less important. For this reason, and the pervasive view that the media is biased (as many journalists themselves even admit on the Pew poll), I think they've seen readerships decline - and rightfully so.
I don't know if investigative journalism has declined independently. What I do think however is that there is far more investigative journalism happening outside of traditional media outlets which has made traditional media outlets considerably less important. For this reason, and the pervasive view that the media is biased (as many journalists themselves even admit on the Pew poll), I think they've seen readerships decline - and rightfully so.