Whilst I agree with you that extending any ruling to Windows Mobile is utterly preposterous, I think your comparison of Nokia's dominance of smartphones to Microsoft's dominance of desktop PCs is equally silly.
Nokia has roughly a 50% share of the smartphone market. Microsoft has an 85%+ share of the desktop OS market. There's also no evidence that Nokia has leveraged its dominance to give itself an unfair advantage over its competitors (that's pretty hard to do when your OS is going open source).
This ruling, as stupid as it is, has nothing to do with Microsoft being an American company.