This isn't about a pure make money online venture, because the particular story refers to the delivery of a physical product. However, it's an interesting read and may give you an insight into selling subscriptions online.
New York Times article
I can see what he's getting at but I don't totally agree. I guess it depends on your definition of "necessity". In this case food is a necessity for dogs because they can't live without it. However, I've had some success in selling useful information to people. Sure, they can live without it if they don't want to pay, but they find that it makes their lives a lot easier if they have access to the info. Perhaps "solve a problem" would be a better way to put it.I think subscription models work best in two instances... Where the product is a necessity or when it’s an absolute passion.