Mobile apps seem like simple systems, but they are often actually quite deep and complex systems, with many different parts that help them keep the appearance of being simple. The user interfaces of applications are the same; they may appear simple, but they are often complex arrangements of screens and dialogs designed to hide the complexities of the application from the user and provide a smoother experience. The easiest way to think about this is that traditional desktop applications and websites tend to be wide, while mobile applications tend to be deep.
This comment applies (on the surface at least) to the navigation of applications. Desktop applications tend to have a central control area where most of the work is done. Think of a document editor--the application centers around the document being written, and you never really leave that area. Instead...
