Kindle sales surely would've increased with or without the existence of an iPad, but I'm inclined to believe they absolutely increased faster with. Personally,

Kindle sales surely would've increased with or without the existence of an iPad, but I'm inclined to believe they absolutely increased faster with. Personally, I sold my Kindle after a few months because I wasn't getting enough utility out of it; after getting an iPad, I've started buying Kindle books again.