If Microsoft wants to sell us on this new feature, they'll have to come up with several real world examples where it would actually make sense. In theory sending computations to the cloud may make sense if it doesn't require sending lots of data back and forth, although nothing comes to mind.
I actually think HTML is a great way for a young person to get started with programming. You get pretty much instant gratification and is very easy to pick up. Once they get comfortable with the basics they can start using JavaScript to manipulate the page. Sure, it's might not be the most "pure" approach, but half the battle is keeping interest.
I'm a software developer and I also enjoy gaming, but 90% of the time I spend on my computer at home is on the web. For that I don't need a powerful machine with a real keyboard. I'd actually prefer to be able to sit on my couch and casually browse the web and maybe play a simple game.
If anything I'd say that tablets are the future of casual computing.