For example, this site. I think all would agree that we have no "right" to its continued existence. None of us pay or contribute financially to this site in any way whatsoever. And yet if PG suddenly changed his mind and deleted it tomorrow, with no explanation or warning - I would consider that to be very poor form, and I'd wager most others here would, too.
Same deal. It's about basic respect for your audience, whether they were paying or not.