It was only a matter of time, and we've talked about it before, there are already ways to fully compose decent sounding music on an iPad (or group of iPads in this case).
The music in the video above was performed using a group of iPad Apps.
Below is what they used:
iPad App with an image of a realistic drum kit that lets users adjust
the kit and tap individual drum pieces to create beats. The drums have
dynamic sounds, meaning that depending on what part of the drum piece
you tap, it will sound louder or softer.
Also see 17 Best iPhone Apps for Musicians