The benefit of buttons isn't in the response time, it's in the tactile feedback that makes it so you don't need 16ms response time. I heard it click, I felt it click, it clicked. If the thing I wanted to happen doesn't, it's because it's broken and not because I can't tell if I clicked the right spot on my iPad. Not having to take your eyes off the road in these cases is the benefit of buttons, and no improvement to response time in touch screens will fully solve that.