Additionally, even if it did need the 10W adapter, you didn't need to order one. All iPads come with the 10W power adapter as per Apple's website:
In the box
* iPad
* Dock Connector to USB Cable
* 10W USB Power Adapter
* Documentation
So there you go. I wouldn't really worry about it. I imagine many people will be using the power adapter with the keyboard so they can charge their iPads while using the keyboard, it likely isn't necessary.