Apple does not allow people who do not have Apple products to download their products many of which are used on iOS devices. Apple has further built up around their iOS platforms with their App store. Unlike with the Android /Google phone users need permission to design an app and even then users have to pay to design their own apps. Developers wanting to create apps for iOS devices need to be approved by Apple to create apps and then must purchase a developer's license for $99.99 and then are expected to pay an annual fee to maintain the license. Next they have to download an SDK, Software Development Kit or for OS X Lion users they can get the free Xcode version, but in order to post their Apps they still need to pay for a developer's license. If a person does decide to sell their App on the iStore they still have to give 30% of their revenue to Apple on top of the developer's fee. The 30% is a standard fee for selling Apps through Google, Microsoft, and Amazon as well. This closed system stifles the ability for developers to be innovate and improve the iOS while also giving Apple a big monopoly. In addition, it excludes people who do not have Apple products from participating in developing Apps for iOS products. This can be a positive thing about because Apple's close system prevents viruses from being spread and also restricts the amount of defective Apps. This allows users to have a more efficient experience on their iOS devices.
That defines it