The freemium model may not work for online education sites but it’s an integral part of others sectors: here are examples of businesses where publishers need to give away something to encourage users to pay for content:

—Newspapers: Just as FT.com and WSJ.com allow limited, try-before-you-buy access to their online news, no newspaper can erect a 100 percent, impenetrable paywall and simply hope readers will pay for access. B2B publisher Emap’s new paywalls allow readers to come in via Google (NSDQ: GOOG) searches because its sites can’t afford to cut off that stream of new users; Rupert Murdoch’s much-heralded paywalls will “not go right to the ceiling”, as the man himself puts it.

—Music: Spotify, We7, Lastfm and Deezer are just some of the music-streaming sites to offer free, ad-supported models alongside paid-for ad-less options, which often throw in offline and mobile listening as a sweetener. The fact all of them have moved to add premium subscription services heavily suggests that despite a growing audience, ads aren’t enough to sustain a music business.

—Games: To counter the threat of games piracy, Finnish developer RedLynx put its new title onto P2P file-sharing sites—but the pirated version lacks the crucial leaderboards where gamers compare scores. If they want the full version, gamers have to pay $9.99 and so far almost 150,000 punters have been happy to do so.