Clay Shirky's explanation is better . If you don't know what you'll get for the money you don't pay. The buyer must be able to predict the outcome of the transaction. No rating system handles this well yet and not many sites tell you what you're gonna get, before you get it. Amazon, of course, is trying hard.
Subscription is a way to let people know what they're going to get.
They've read one issue of a magazine and therefore have a pretty good picture of what they are paying for. The default of any framework identification service should be anonymity. It means you should have a different ID for every service you access. That way the service provider doesn't know who you are but is still able to serve you, using very sensitive data without risking your integrity or privacy. Many services, that MS won't dare to implement, are made possible this way.