Two years later, looking back at my own question and the comment by @kuchitsu, I may have understood why I thought 正規品 means different from the given example.
comment: some info and examples: ejje.weblio.jp/content/%E6%AD%A3%E8%A6%8F%E5%93%81 – kuchitsu Jan 29 '18 at 18:24
As per referenced comment, 正規品 on Weblio hinted that the word does not simply mean 'genuine products' or 'real products' by default. Other translated meanings found in the list: correct parts, official products, box, retail.
[There] are many words that begin with 正規, which mostly translates to 'regular' or 'normal'. That has nothing to do with 'genuine'.
Such varying translations may suggest that some retail products--notably OEM (manufacturing)--can be considered as 正規品 in appropriate context. OEM products should be understood as "products that comply with certain specifications" rather than "products that have been made exclusively by the rightful owner".
That might explain why 正規品 is mostly translated as 'regular' or 'normal' rather than 'genuine' as noted in the question.
So what does 正規品 mean, really?
The included word 正規 might further explain why there are varied meanings as discovered above. From 正規 on Weblio, the word has mainly two branches of meaning: 正式の (regular, formal, proper) and 合法的な (legitimate, legal).
The given example of "Windows is not Genuine" was translated from the latter branch of meaning, which is 合法的な (legitimate, legal). Therefore 正規品 can be translated as "genuine product" in this context; however this should not be taken literally as the translation may vary by context.
Another word usage may be found in some product reviews. For example, a retail plastic model kit usually consists of molded parts surrounded by the frame that is known as "runner" (see Plastic model and プラモデル on Wikipedia). Such unassembled parts in the retail product can be referred as 正規品 also.
The later example of "runner" was translated from the former branch of meaning, which is 正式の (regular, formal, proper). Therefore 正規品 can be translated as "regular parts" in this context, which differs from and not really "genuine products" that otherwise understood in the previous example.
I am looking for an answer that can explain the meaning, as well as the usage of this word i.e. whether 正規品 is a technical term in some fields, abbreviation of a more complete term, or something else that I may have missed.
The given example is likely intended to show some research effort; however that might also have caused people to answer solely based on the given example and disregard the context, unfortunately.
Hence the two branches of meaning may give different meanings as above. If one must have a generic translation for that, then 正規品 may be translated as "standard products". That seems close enough to contain both meanings with given context.