Do ebooks cost a similar amount to print books? If you limit what you're buying to recent bestsellers and the like, sure. But many ebook sellers, including Amazon, routinely have massive sales. I've bought ebooks for $2 or $3 apiece. I don't see similar discounting for physical books unless they're secondhand and well-worn--and usually even in that case the price doesn't go so low.

I use ebooks for books I think it's less likely that I'll reread, when I can get a bargain.