If you store anything on the cloud, you sort of have to use a subscription model because they may have to keep your data around. They have to make sure the inte

If you store anything on the cloud, you sort of have to use a subscription model because they may have to keep your data around. They have to make sure the interface works, that bandwidth is paid up, that they are compatible with new browsers and so on. That is why most cloud companies use subscription. If you have a service which is a one off: you upload data, it processes it, and then you download it, it might be possible to just keep charge as a one off.