If there's a way to read the book, the book can and will be copied. It doesn't matter if it's DRM protected with 84 bazillion bit encryption, if there are dead trees involved, or anything else. You can make it harder to copy, but copied it will be.

Mass piracy will continue full steam ahead at current rates.

Most of these sites allow you to read on a computer screen and those can be captured and OCR'd. And if they don't allow that, you can take a photo of your device and OCR that. And if you can't do that, you can manually type in the book. There's always a way, and it will always happen to any books that publishers are making any kind of profit on.