If you are considering an iPad2 for musical/audio purposes...don't hesitate, this is where the device is at its best. The OS has core audio and MIDI drivers, these features being usable via the USB port on a camera connection kit. I run mine to a usb hub and then to a MIDI interface and USB mixer. This allows me to play hardware synthesizers using the touchscreen as an interface using the app "thumbjam". The Moog app you mentioned is great, KORG has several great iOS instruments; there is multi-track recording, sequencing, effects and synthesis software that is quite fleshed out at this point. Musicians are among the few who truly benefit from a tablet form factor, with few caveats. Android does not have a low latency audio subsystem, much less MIDI and USB audio drivers for hosts of devices.
Here is a list of devices that are USB class compliant and work with iOS: http://iosmidi.com/devices/
The iPad 2 is my first and only Apple product, I chose it over the competing alternatives simply because it CAN perform the tasks I desire. A computer is only useful if it has software to support the tasks you intend to perform. There is no other mobile option (for the moment), so the fact that it also happens to be cheaper than the lesser spec'd competition only makes the decision easier.