Kutcher was probably chosen in large part because he looks a good bit like the young Jobs: http://cdn.macrumors.com/article-new/2012/04/ashton-kutcher-.... For better or for worse, physical resemblance seems to be a large determinant in who is cast to play characters based on real people, not whether their previous acting would fit the target persona. Look at Social Network or any historical film for more evidence. They try to match up visages because that is what's obvious to filmgoers.

(Months ago, a techie friend mused to me that young Steve Jobs did look like Kutcher, so the casting isn't a total shock.)