This is part of the new naming conventions for pork parts. They, whoever "they" are, decided to use a nomenclature that is more consistent with that of beef. See the loin section part of this chart:
https://www.porkretail.org/filelibrary/Retail/NPB Nomenclature cut chart 041913 HR.pdf
http://www.meattrack.com/urmis/common-names/
Here is a Rosetta Stone (but only the "best parts" of the loin; it doesn't go back as far as the "sirloin"):
http://www.porkandhealth.org/filelibrary/PAHGeneral/FactSheets/pork_names_infographic.pdf
Oh... here is article that defines "they" and the new scheme:
http://articles.chicagotribune.com/...403_1_national-pork-board-pork-cuts-pork-chop
http://www.npr.org/blogs/thesalt/20...me-is-porterhouse-chop-i-used-to-be-pork-chop
https://www.porkretail.org/filelibrary/Retail/NPB Nomenclature cut chart 041913 HR.pdf
http://www.meattrack.com/urmis/common-names/
Here is a Rosetta Stone (but only the "best parts" of the loin; it doesn't go back as far as the "sirloin"):
http://www.porkandhealth.org/filelibrary/PAHGeneral/FactSheets/pork_names_infographic.pdf
Oh... here is article that defines "they" and the new scheme:
http://articles.chicagotribune.com/...403_1_national-pork-board-pork-cuts-pork-chop
http://www.npr.org/blogs/thesalt/20...me-is-porterhouse-chop-i-used-to-be-pork-chop
