Re: As I have said a million times
iOS has always had low latency, and Wireless MIDI baked in. Compared to the price of specialist audio control surfaces at the time of its release (low volume of sales usually results in higher prices) the iPad's price looked more reasonable. And multitouch is a good UI for virtual mixing desks. I've seen a few bands in pubs using a virtual mixer on an iPad - the advantage is the soundman can stand amongst the audience and adjust levels accordingly.
True, most iPads aren't used for this, but there are lots of niche applications instead of one 'killer application'.