Not really. It is just translating the Windows system API calls into Linux system API calls. It's not emulating Windows, it's an entirely different implementation that doesn't necessarily match that of Microsoft's implementation. It had it own workarounds to make buggy code work.
You wouldn't call a Java Virtual Machine an emulator of another JVM either, they're just different implementations of the same specification.
And a 5th: Advertising.
This will level the playing field a lot since Google wouldn't be able to subsidise their browser with ad money in order to show more ads in their search engine as well as feed their ads with data from the use of all their products.