iPhone had the first two store UIs; the iTunes Store for content like music and movies, and the App Store for software. The iPad will add a third, the iBookstore, for buying eBooks. These stores all provide content for users to extend the utility of their device. But each has a pretty different user interaction model for accessing, purchasing, and consuming that content.
- The iTunes Store is a separate app that is completely distinct from the iPod app. When you find something to buy, prompting you for your iTunes account password. It then adds the purchase to the app's Downloads tab. Once you have purchased the content, you must then switch back to the iPod app to listen to or watch it.
- The App Store is a separate app. When you purchase something, it prompts you for your iTunes password, and then exits to the home screen, switching to the screen where the app will live. The state of the download is reflected in the app icon. When the download is complete, you tap the icon on the home screen to use it.
- The iBookstore (the one word is the official name as used by Apple) is not a separate app, but lives within the iBooks app on the iPad. Purchasing content prompts for the iTunes password and downloads in-app, which can be directly accessed after it has finished downloading.
Each type of content follows a different workflow when going from access to purchase to use. If a goal of the iPad's low price is to drive content sales through the three stores, as some speculate is the case, then the purchase model should be as streamlined for the different types of content. Forcing different workflows will only confuse users who can't remember which type of content comes from where.