What you're talking about is not plagiarism. You're referring to duplicate code, but you (general "you" this time) have no idea if the duplicated code is taken before or after reading the other responses. If you go to SoPW, there's a reply link -- so you can reply to a question without reading other responses.

If someone asks how to print a "Hello, World" string to the screen, there may be many responses of print "Hello, World". If someone asks how to write a Schwartzian Transform, I'd expect a lot of duplicate replies as well.

Plagiarism is the act of willingly copying information without citing the source. And I feel you're using a name that most associate with "bad, evil, wrong" incorrectly.