ok so webster's dictionary says:
1 : one that possesses, owns, or holds exclusive right to something; specifically : PROPRIETOR 1
2 : something that is used, produced, or marketed under exclusive legal right of the inventor or maker; specifically : a drug (as a patent medicine) that is protected by secrecy, patent, or copyright against free competition as to name, product, composition, or process of manufacture
3 : a business secretly owned by and run as a cover for an intelligence organization
that means, Linux is proprietary to GNU (wierd terms -yes, but still a copyright...), Mac OS is proprietary to Apple, Windows to MS...
HTTP is not proprietary, TCP/IP is not proprietary, USB, DVI, ODF, etc...
and just for the record, macintosh software stack =
1.) cross-vendor openfirmware / intel efi
2.) opensource darwin kernel and system libraries (UNIX spec 3 compliant as the article states) and x11 window mgr
3.) closed source gui, closed source system libraries and frameworks like quicktime, core data, etc...