Linus cooking up Git - that's not a side project; that's what he does for earning a living. They needed Git as a replacement for BitKeeper. I do admire Linus, when he sets his mind on something, he gets things done.
But, about people working for big companies, since you are talking about iOS / WebOS, etc... these people do many times have side projects, but they are internal and in the context of the company they work for, not public. And the cool thing about a big company (versus a startup) is that deadlines are more relaxed (you do have more free time) and you can switch projects when bored to death.
Git is Linus's real job? Slacker. He needs to do an HTML5 app some weekend, and put it on GitHub, to show he has actual dev chops.
these people do many times have side projects, but they are internal and in the context of the company they work for, not public
I don't think most ppl would consider them side projects, at least not in the discussions ppl typically have. For example, I've seen people say that it literally has to be on GitHub.
But, about people working for big companies, since you are talking about iOS / WebOS, etc... these people do many times have side projects, but they are internal and in the context of the company they work for, not public. And the cool thing about a big company (versus a startup) is that deadlines are more relaxed (you do have more free time) and you can switch projects when bored to death.