Perhaps the benefit of eInk readers is a combination of features rather than any individual feature.

Almost any device with Internet access makes it far more convenient to access most contemporary or public domain books, as well as a great deal of what falls in between. It doesn't matter if you're a book buyer or a book borrower (via libraries, of course).

Eink readers also provide far fewer distractions than computers or other mobile devices. I'm not going to chalk this up to the reader's inability to focus. Even with print books, many people prefer a quiet room or a place with social boundaries (e.g. a park or transit) to a bustling environment. Most mobile devices and, alas, current trends in computers also bring things to the user's immediate attention unless configured otherwise.