A generic term that wasnt in common use before Apple (unlike, say, the term windows). In fact, the term apps wasnt even used much pre-iPhone.
AFAIK, Microsoft have never sold windows, nor have they gone after anyone who manufactures or sells Windows.
If Microsoft ever did go after and try to stop windows sales companies from calling their windows "Windows" then people could complain. The "Windows is generic" argument would only make sense if Microsoft were in the glass window indistury.