This is true in small ways and large ones. Some people talk about how you can so easily write in the things — underline, comment, whatever — and sure, I guess you can, if you happen to have a pencil or pen with you, and if you can write really really tiny. And then once you've written your notes, how are you going to find them again? Do a search? That's not happening. Some people say, well, you can note down the key passages in the back of the book — and again, that's right, if they give you some spare blank pages back there, and if you don't mind making every notation twice.
But those are relatively minor considerations. The big thing is this: you can't read the damned thing without using two hands. You hold it in one hand and it just closes over your fingers, which is great if all you want to do is read the front and back covers. And that's just if you have a "paperback." If it's a "hardback" it's probably going to be too heavy for you to hold with one hand for five minutes, and if it's a big book you won't be able to do it at all. Can you imagine trying to read a book version of, say, The Lord of the Rings or Infinite Jest? Ridiculous.
So if you don't ever want to lie on your side to read — I tried that once, and it only works if you're willing to prop the thing precipitously at some weird angle, or else turn over on your other side every time you get to the end of a page — or to sip a cup of coffee or eat a bagel as you read, you're golden. And if, when you're reading a book you need to annotate, you can always be at a desk or table with a pencil in your hand, and can write with one hand while you try to hold the book open with the other one . . . well, you get my point. As I say, there are some good things about books, some very good things, but right now the technology just isn't mature enough to make it usable. Check back with me in another decade and we'll see what the geniuses have been able to do to improve it.