This concept of Universal Design is not so much a one size fits all as it is an attempt to make a product or process accessible to everyone. It's a new way of looking at the environment surrounding us and trying to ensure there are as few obstacles as possible to inclusiveness.
So, for example, it is a simple matter when roads are built to include curb cuts in the design:
These allow people in wheelchairs to move about their neighbourhood. But, as is sometimes the case, they have become useful to others: people with strollers or shopping carts or bicyclists.
You may have have seen the evolution of traffic signals in your neighbourhood from this:
to something more useful to all:
The addition of the chirping sound in some location benefits the sight impaired.
With books, the increasing availability of audio-books adds another dimension and more accessibility. Some popular books, mostly those available through the school market are released in two versions, one with what is called a lower readability. This involves someone, the author or editor, adapting the vocabulary, the spacing, the font and adding sidebar or footnote explanations, all to assist what is, perhaps unflatteringly, called the struggling reader.
Another recent example is the development of e-readers which have a feature that allow the size of print to to be increased. If you have ever squinted at some of the older 'pocket books' that have reduced font to fit the material into a small size you will appreciate this feature.
It can be an interesting exercise, maybe a future career, to consider how obstacles to use can be redesigned. It's also a small reminder that we are making progress.