http://usability.com.au/2005/10/disabilities-and-technologies-2005/
in the article he mentions that there is an average of 10 to 20 % of disabled persons in the western countries. all of these persons have problems(big or small) working with the standard tools and interfaces. he then lists some tools that were designed for these persons like visual keyboards, headwands, switches,…
20% of the population that has some disability, is quite a lot actually. it means that whatever we make, we have to take the disabled into account because they aren’t a negligable minority.
User Friendly Planning in a Center for Non-Congenital Brain Disorder 
I’m very surprised to see these high percentages. But again how does one objectively determine if someone is disabled? In any case it’s worth knowing that 33% * 20% = 1/15 people have a e.g. sight disability and this will only increase in the future.
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I think that Andrew just asked the main question on this subject. In the article, it says that the study relies on self-reporting (or a reporting by their carer) instead of objective data by an independent person.
Also, the conclusion of the study doesn’t separate age groups. This was also part of the article:
“Less than 4% of children between 0 – 4 years had a disability; for people 35 – 39 years the rate is about 15%; for those 65-69 the rate has increased to about 40%; the rate then increases rapidly to more than 90% for people 90 and over”
This also explains why so many people have sight disabilities.
The number of reports of disabilities is indeed still increasing. Maybe people are not as ashamed to report disabilities as they would have been (let’s say) a decade ago? (The study looks at a time span of 3 years) Maybe disabilities are better recognized then several years ago and also reported?
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