They have the same number of words, they tell the same story, yet they are often half the price. Ebooks are so much cheaper than paper books. And they should be - you can't pass them onto friends and you can't store them on your bookshelf. 
Personally, I still read mostly paper books, but occasionally a link crosses my tablet and I get the whiff of a read that looks interesting. I read the blurb, the reviews and then I look at the price. If it comes under the cost of a coffee and a muffin, I usually hit buy because I figure it will bring me as much pleasure as a seat in a cafe. Surely any read - even if I don't finish the book - is worth the cost of a muffin and coffee? And I love coffee and muffins. 
This is why our ebooks, at £2.99, cost barely more than a tall latte at Starbucks (the 'barely more' is the 20 percent VAT). Sometimes retailers make our titles even cheaper by offering them at 99p but, unless they promote the book to their loyal customers, these discounts don't bring in much profit. Retailers take more than 50 percent of the price, so 99p really does leave us with pennies on our investment.
But no matter, we are happy with every sale. We want to proliferate the web with our ebooks, keeping costs in check with the coffee and muffin test. But one day, I might have coffee, a muffin and an ebook.