If you look at the actual trademarks you will see that there is no registration for Operating Systems. Trademarks are only for specific goods and services, you can't globally prevent use of a word.

[1] http://tmsearch.uspto.gov/bin/showfield?f=doc&state=4806:754... [2] http://tmsearch.uspto.gov/bin/showfield?f=doc&state=4806:754... [3] http://tmsearch.uspto.gov/bin/showfield?f=doc&state=4806:754...