Sure, this is a good question. But are really we talking about the same thing ? An iPhone app to control a cockroach and animal farming to produce food ? Why an iPhone app, BTW ?
And why not an iPhone app? Hackers don't need a reason do something new. A simple reason I can think of is to demonstrate that this is possible and also get people interested in the field so that more research is done. I would very much like to see computers directly connected to human brain and I/O being done on it in the future.