Yeah, Mr. Kay is just blowing his own opinionated air towards everyone. I disagree strongly with him, but unlike him, I'll give details as to why his opinion is BS, and mine is right.
First, as at least one other forum member above has stated, iOS is much simpler than "mouse" computing, and therefore has opened up computers to many, many more people. For example, a few years ago, my 2 year old son was using an iPod Touch perfectly easily and on his own. Why?!? Because he understood intuitively how the system worked because it was so straightforward and simple. He only picked up how to handle a "mouse" computer at about 4.5 years old, and then with a lot of frustration and needing frequent help. I have some non-computer older friends who also were able to learn iOS device operation extremely quickly, whereas computers confuse them. I've heard stories like these above from countless friends of mine.
Mr. Kay can say that iPads suck all he wants, but the pervasive evidence above pretty much torpedoes his opinion as being worth much. If you can open up the power of computers to a wider range of people, including the communication, knowledge, and entertainment aspects that they possess, you're doing a good thing for the world.
Now, he might have something of a point that iPads/tablets are not great at Authoring content. But then again 1) they never claimed to be great authoring tools (although the communication aspect of them betrays that idea somewhat), and 2) they are claimed to be consumption devices (knowledge, books, internet, entertainment, etc.).
Second, Apple's creation of tablets was a very intelligent bet on how to compete with low-end PCs that don't have any margin/profit. They realized that probably a majority of low-end PCs are used for content consumption (games, internet, netflix, etc.), and not content creation. If you could provide a well-built, but relatively inexpensive, light, long battery life, hold-in-one hand with an operating system super easy to use tablet with a fantastic screen, at about the same price as those low-end PCs, and infuse it with a rich ecosystem (iTunes, AppStore, iCloud, etc.), and still make crazy profits with it, well . . . not only have you given your company a huge leg up (as low-end PC makers like Dell start to go out of business), but you've provided a superior and mobile experience to the end-user as well. Hell, with an iPad, it's now simple to sit in bed and get your morning news and e-mails while sipping your coffee--instead of waiting for the laptop that weighs 3 times as much to boot up, or trudging over to the study to sit at a desk to use my desktop.
Mr. Kay seems to have an extremely narrow view of things, and doesn't give details. Glad he wasn't in charge of Apple.