According to the Pew Internet & American Life Project the internet is now the third most popular news platform, see their study entitled Understanding the Participatory News Consumer. The internet is third behind local and national television news. It is a ahead of national print newspapers, local print newspapers and radio. To me this is substantial.
Also in their report is that 6 in 10 get news from a combination of online and offline sources on a typical day. As I read news on my mobile device I realize too that I do not consume as much news with a newspaper as I once did, or as my father did. To reach me through advertising it must be online, otherwise I am an unreachable demographic. More individuals are fitting into this category daily.
In my opinion a marketing campaign used to be a mix of different forms of media to reach a demographic, such as print, radio, magazines, newspapers. However these days I believe it is entirely possible that some demographics can only be reached by one form of media, online media. My two cents.
Their report is excellent, take a look through the link above.