Relevant interview with the Economist's guy in charge of digital (overall a fascinating examination of how they're evolving): http://www.niemanlab.org/2015/04/the-economists-tom-standage...

    The Economist has taken the view that advertising is nice, and we’ll certainly 
    take money where we can get it, but we’re pretty much expecting it to go away.

    So a majority of our revenue comes from subscriptions, and always has. The 
    proportion of revenue that’s coming from subscriptions is going up, and 
    will probably continue to go up. So I’m very very happy that that’s our 
    business model, because I think that’s sustainable. People do seem willing 
    to pay for our journalism, and our digital subscriber numbers are going up 
    very nicely.