Usability is indeed a very big issue, and what you have said here is more profound than many people will realize. People with all manner of disabilities - physical disabilities and learning disabilities - are people outside of the statistical 'norm' of the population. But they have far more potential for success and achievement than they can find in the things that are designed for the 'norm' by the 'norm'. It can become a road that leads in two directions: one path is taken by falling behind in school, in work, and in life. The other path is taken by finding other ways to do things that work outside of the 'norm'. That's why such a high percentage of successful entrepreneurs also have some kind of disability (typically a learning disability) to live with. The list of people who have found their own success despite such a disability is astonishing, and includes many of the people we consider as having made the most profound contributions to technology, society and culture. Imagine how much longer that list might be if we designed our world so that everyone was able to achieve their full potential by being able to use whatever they needed to use and no-one was left behind.