Understanding that it was more than just the story I told but the reading experience that made impacted the book. The more I learned about not just writing but publishing I began to understand that colors, fonts, size, spacing, etc. really matter for the readers enjoyment. While you never can make a book perfect for everyone, you don't want the majority of readers to say, "I loved the story but..." and then go on to explain what they didn't like as in the hard to read font or the size couldn't be changed on their reading devise. You can't judge a book by it's cover, but you can influence it's appeal by it.
While I've never researched their impact, I like to believe more people are reading because of these other options. We don't always have time to sit and read at home, but the option of having a book while waiting in a doctors office, parking lot, etc. are good moments to "flip" open a book. Also, with text books and manuals, the ease of accessibility is a plus.
While I've only been writing "professionally" for a year, I have been writing/storytelling for as long as I can remember. I enjoyed writing for myself, but storytelling is taking others along for the ride. Seeing them picture in their minds the story, the characters. Being an author isn't telling the story, it's engaging the reader in the pages with you.