Computer Network Freaks

Why we need layers in computer networks???

I always wondered,why we need layers in computer networks???
We have heard about the layers like Link layer,Network layer,Transport layer,Application layer but why???

• Application layer - User Interface in networking will be taken care by it
• Transport layer - Takes Responsibility of communicating to a specific process in a computer connected in the Network
• Network layer - Takes Responsibility of Routing
• Link Layer - Takes Responsibility of delivering message to specific computer in a Network
• Physical layer - Takes Responsibility of converting data into bits and sending them through a wire.

Saw?? How our life is easy?? We divided Tasks and each layer is responsible for its task.