I'm purely speculating, but I think they are appealing to the wider audience because of the 'cool' factor. They've been successful because of the way Apple positions the device. It's just a cool toy made by a company with a cult following. You use it to impress your friends, your coworkers, and probably because you want everyone else to think you're a geek that's into the latest tech. In short, it's a status symbol.
It doesn't offer anything new in terms of functionality. Everything you want to do in an iPad, you can also do with a modern laptop. Ok, laptops can't do touch screens, but I'll argue that it's not really novel functionality. In fact, as Brydge's Kickstarter campaign has shown, it comes with reduced functionality.
Let me stress that I'm not belittling the device. I'm sure it also has a lot of great technological feats packed into it. Only that it's secondary to the social/marketing factor.