I've also seen elsewhere that that increase in YA sales may not necessarily be related to young adults. Good books are good books, and it shouldn't matter if it was written for younger or older readers, now ability matters, but it can be good for the reader to not struggle all the time, so an adult or older student reading a children's or young adult novel can still be good and fun. Yes, people should be challenged, but not all the time, it is also good practice to do things that have become "easy" - you still can cook and enjoy a grilled cheese sandwich, just cause it is easy to make doesn't make it taste bad or be bad for you.
For many though, I'm sure that the book anonymity that can be achieved by reading a book on their device has opened new options for what to read. Since no one notices that you are reading Chomp, Wildside, or the Hunger Games, then no one judges. So use your ebook device to explore new options of reading. I've found many new authors whose book covers I'm not too comfortable with, but whose content is wonderfully written. Here is one example that I've experienced. A long time ago I read Agent of Change, a wonderful science fiction story that attracted me right away with it's cover (who doesn't like a giant turtle?), great story, wonderful characters, and well written. Then one day the authors received a romance award, they re-ordered the authors, and changed all the book covers, so that when I was checking to see if I already had a book in my collection, it didn't show up. The story is the same, but perhaps some people would feel put off by one cover or the other. Either way, enjoy what you read, and keep an eye out for more.