You wrote, "Plus, although you can paste something on the main clipboard multiple times, Yank removes the text from the kill ring, so it can’t be yanked again." I don't find this behavior to be the case generally. You can yank text multiple times in emacs, and I confirmed kill and yank in Pages, Terminal, TextEdit, TextWrangler, and Safari work the same way. The only thing that erases the kill ring is a kill that's not immediately preceded by a kill.
This brings up a second point that wasn't mentioned in the article. If you perform multiple kills consecutively, after the first kill, text is appended to kill ring, allowing you to place a section of text consisting of multiple lines into the kill ring.
This brings up a second point that wasn't mentioned in the article. If you perform multiple kills consecutively, after the first kill, text is appended to kill ring, allowing you to place a section of text consisting of multiple lines into the kill ring.