While there's overwhelming similarity between the operating systems in most cases, there are also a lot of differences. As you probe more into the differences, you find that they emerge from deep-seated disagreements. Some are disagreements over development methodology, some over deployment and usage, some about what's important, some about who's important, and some about which flavor of ice cream is superior. Just comparing the surface differences doesn't tell you anything; it's the deeper differences that both explain and justify why each group does things the way they do.