The instructions on Code@ExactTarget say I should make two apps, but I'm only developing one. Why do I need to make two?
This answer descends from Apple maintaining two distinct environments for Push Notifications - sandbox and production. Since each environment requires it's own set of credentials, and only one set of credentials can be associated to a single Code@ExactTarget app at a time (one per platform, that is). So a single APNS Certificate and a single Android GCM API Key can only be associated to a single Code@ExactTarget app at a time. From there, it's best to have a different development and production setup, so a second app is needed to manage the other set of credentials.
As a reminder, Apple's Sandbox and Production environments are incompatible with each other, so the token separation is important to maintain, and it's important to ensure that the right credentials are being used in the SDK configuration for each build type.
More information on app registration is available here: