In an interview Sunday with Business Week, Phil Schiller, Apple's senior vice president for worldwide marketing, defended the company's policy of selecting which applications it allows in the online store.

A Store 'People Trust'

The intention, Schiller said, has been to build "a store for the most part that people trust." This has meant being highly selective about what applications are accepted. The App Store now has more than 100,000 apps, more than any other app store for mobile devices, but it's also dealing with about 10,000 new submissions every week.

Schiller said the store's role is to decide which products end up on its shelves, much as any quality retailer would.

Apple has said app rejections that have gained attention in the developer community are mostly for technical reasons. According to Schiller, the rejections have included apps that help steal content or personal information, as well as apps with illegal use of trademarks or with inappropriate content.

To deal with apps that are accepted but whose content is not for kids, the App Store has added parental controls to block certain titles. These include apps with adult content or depictions of violence.

This gatekeeper role by the maker of the device does not exist for the unlimited range of software that is available for PC or Mac users. However, the market for third-party applications for mobile devices was fragmented until Apple demonstrated the value of an online store.

From 70 to 20 Percent?

At the same time that Apple is facing these issues, Google may be seeing an opening for its growing Android platform. While the Android Marketplace has only about 10 percent of Apple's App Store offerings, it's growing rapidly and developers are considering porting or developing apps for Android in addition to other platforms. Virtually every other major platform and several wireless carriers have also opened their own app stores, such as the BlackBerry App World.

Some industry observers are predicting Apple's App Store will slide in market share from about 70 percent now to as low as 20 percent within three or four years.

Al Hilwa, program director at industry research firm IDC, said developers' allegiance to a particular app store is driven by the projected stability and installed base of that platform.

As the iPhone "has been established and had a competitive advantage," he said, developers have flocked to the App Store. But, Hilwa noted, Android "has the most momentum" right now of any competing platform, particularly in the U.S., with OEMs stepping up their commitments and product releases.

Hilwa expects the application portfolios of each platform will increasingly become more balanced, with most of the major iPhone apps ported to Android.