Tell that to NASA. Laptops on the International Space Station are going to be fitted with Debian 6. Windows is done on the ISS.
Not for reasons you think. They can modify and tweak Debian code for their needs and not windows and they have ability to write custom apps for it. This is far beyond average user ability.
Yes, you're correct. I had heard some stories about a virus issue, but that's not substantiated.
But that's an advantage of using Linux over Windows. Not everybody needs it, of course, but some do, including my employer, an office phone systems company. We use both Windows Server and Linux in our products, and Windows will be going away in the next year or so due to high licensing costs. That's another Linux advantage, especially in business (but not in the consumer space, where Windows is preinstalled on PCs and the lower single-machine licensing costs are factored in).