It's for quality control and security and it's good business. When they decided to do this in 2008 they couldn't have known how big the App Store (and the iPhone) was going to get. You can listen to an interview a WSJ reporter did with Steve Jobs about it. No one at Apple actually knew, including Jobs.

https://www.wsj.com/articles/the-mobile-industrys-never-seen...

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MR. WINGFIELD: What does that number say to you?

MR. JOBS: It says the App Store is much larger than we ever imagined, iTunes has been out for over five years. In 30 days, users downloaded 30% as many apps as everybody in the world downloaded songs from iTunes.

MR. WINGFIELD: What did you expect? What was your internal...

[crosstalk]

MR. JOBS: We didn’t expect it to be this big. The mobile industry’s never seen anything like this. To be honest, neither has the computer industry. [laughs] 60 million downloaded applications in the first 30 days. 30% as big as iTunes song downloads during the last 30 days, this is off the charts.

MR. WINGFIELD: OK. The 70-30 split, are the economics of this working out the way that you had said when we last spoke, which is that you might make some money, but you don’t expect it to be a big source of profits?

MR. JOBS: Yeah. It’s just like iTunes.

MR. WINGFIELD: Even with the huge popularity of this, you don’t...

MR. JOBS: No. It costs money to run it. Those free apps cost money to store and to deliver wirelessly. The paid apps cost money, too. They have to pay for some of the free apps. We don’t expect this to be a big profit generator. We expect it to add value to the iPhone. We’ll sell more iPhones because of it.

MR. WINGFIELD: Every time I write about the amount of developer support that you have on iPhone, I hear from a bunch of other people who have been doing BREW applications for years. People say, “No, this is nothing new. There is a whole ecosystem around Windows Mobile, around Java, BREW, for other types of phones.” How do you think these apps compare to those?

MR. JOBS: Two or three things. No. 1, if you talk to developers that are developing for the iPhone, what you’ll hear from them unanimously is two things. There’s never been a mobile platform that’s been this powerful before.

As an example, when we were working with some of the first developers under the radar before we launched, they first sent their mobile teams here. When they realized how powerful the platform was, they sent their desktop teams here or their console teams here.

They realized that the quality of the graphics, the animation, the processing and the memory really made this much more capable as a platform than any other mobile platforms. We’re hearing that from every developer. You heard [videogame designer John] Carmack’s comments, right?

MR. WINGFIELD: Mm hmm.

MR. JOBS: The second thing we’re hearing is that the development environment is far more advanced than they had ever seen on a mobile platform before. The APIs are in another league, the whole development cycle, the debug tools, etc. That’s just to develop the app.

Once your app is developed, to be able to submit it to Apple and have us take care of all of the marketing, wireless distribution, billing and all the transactional stuff for you, and deliver it right on the handset, that doesn’t exist today. There are some websites that will do some of that for you. They don’t deliver it to the phone.

MR. WINGFIELD: They go and...

[crosstalk]

MR. JOBS: Yeah, they’ll deliver it to your PC. You can sideload it, this and that. They charge a lot more than we do for doing a fraction of what we do.

MR. WINGFIELD: Do you know what the revenue split is on these other sites?

MR. JOBS: The minimum is 50-50. Generally, it can go into the 70% or more.

MR .WINGFIELD: On the other side of the equation, 70 to the distributor and 30 to the developer?

MR. JOBS: Yes. It’s at least 50. We’ve heard it goes up to 70. They do a lot less than we do. They don’t get it in front of every user. You have to go to a website. You have to buy it on your PC, blah blah blah.