The major challenges in this youthful field of machine learning are building appropriate hardware and making it work. That, so far, has kept it the domain of the software engineer. As the situation continues to stabilise this is going to become the playground of statisticians and analysts.
Or to put it another way - if you compare any field to software engineering, the problem is that other disciplines have a much harder time debugging things. Software is almost unique in that debugging is cheaper and quicker than building things right the first time.