Apple adds a lot of value via the App Store for initial app purchase/download.
I agree they add very minimal value for recurring subscriptions, and their fee should be dialled back to be inline with what card processors charge (because they're essentially offering payment processing and not much else).
The app store provides value to customers for recurring charges by being a MitM and offering an interface for recurring subscriptions. I can go to the recurring charges bit of the interface and see all the apps that can charge me.
I never give CC info if I can help it. Once you give out your CC info, you have to be eternally vigilant because they can charge you on their terms. And to cancel, you have to hop through whichever hoops the company demands of you, like requiring a phone call.
For example, I would never have taken up Youtube's 3-months-for-$1 trail last week if I had to insert my CC info. I was only open to the idea because it went through Apple's payment system and it's easy to see that I'll be billed in March if I don't trivially cancel the subscription from the iPhone interface.
Since the app store billing system is the reason I coughed up the money to Youtube, it certainly makes sense for Apple to get some of that money. And I could make a case that they deserve a cut for the entire lifetime of my subscription.
I almost exclusively deal with subscriptions through Apple. Dealing with multiple vendors is a pain and Apple adds a high level of service and security.
If you think your random app company is getting permission to do recurring billing, think again!
I agree they add very minimal value for recurring subscriptions, and their fee should be dialled back to be inline with what card processors charge (because they're essentially offering payment processing and not much else).