Last one of these for now - I've run the Google reading age numbers for the main US news sites too, with the results you see to the left.
"Main" US news sites in this context are a combination of the Hitwise and Nielssen data as reported in Pew's State of the News Media 2010 report.
Confirmation of the expected includes business and finance websites using the most challenging language (less basic, more intermediate - almost no major site uses much advanced language according to this schema, except Facebook). By this point I'm not surprised that the aggregators come out using more challenging language than their constituents - I can't yet account for it, but is seems to be consistent across the board.
That the Washington Times and LA Times use almost the same complexity of language as Fox is more of a surprise, but living in England I know Fox only through its abominable reputation. Perhaps American right-wing demagoguery is more articulate than ours.
Finally Topix, the local news aggregator, is also notable for using more basic language. Which means this exercise probably isn't over and sometime in the coming week I'll be taking a look at how local news sources compare in their complexity of language too.