MS is following Apple and Google in offering a free OS. Well, free upgrade anyway. W10 will in all likelihood be the last Windows that is not completely free. MS will make money on their app store, enterprise services and cloud services like Azure.
Using XP today is like using a horse for transportation in the age of the Tesla. Sure, it will get you where you're going, and if that's the only thing you want then XP is ok, but it won't get you there fast, and not in style.