Every single operating system out there has a target audience. You'd be suprised as to how many folks out there use something different then Windows. It just doesn't fit everyone's needs and requirements. Myself, I'm a LAMP (Linux Apache MySQL PHP) developer. I create web app/sites using free yet very efficient technologies. There is also more functionality offered using LAMP then using the web technologies offered by Microsoft. If you are curious to know why, it's because Microsoft sells closed-source software (ie, the developers at Microsoft are the only ones who can add said functionality into the package). While using open source software (ie, Linux, Apache, MySQL, PHP), a community of individuals develop the software. What's nice about this is people from all across the world help develop the functionality. So instead of maybe 1000-2000 developers working on a particular item (ie, Asp.NET (I'm just taking numbers out of the blue, it's probably not very accurate)), there might be 10x that amount, give or take, which are working on building functionality in PHP and it's extensions.
I also dual boot my system. I rarely play games, I primarily use my computers for work. Could I live solely off Linux. I don't see why not. Then again, I do have years of experiencing with it. For someone new to Linux, it can be a daunting challenge. But I'm sure when you first touched Windows it felt just as intimidating.
If it helps, I have over 15 years of using Windows, and over 10 using Linux. And I'd take using Linux over Windows any day. Why? Because I like the feeling that I'm actually in control over my own computer. I know exactly what's going on. With Windows, I always feel there is a lack of control. Plus, with the history of Microsoft, I tend not to really trust them all that much.