It must be something from copying from the vBulletin editor, then, rather than a Word processor, because I'm not certain anyone actually did it from a Word Processor, though it is possible. And while some may have used a processor and some did not, the two extra line breaks appeared in every single product upload, so perhaps it was simply the pasting that added the extra breaks that did not show up within the editor.
The difference is that even with the fix as it is now, we can add line spacing within the editor as necessary and it shows up exactly as it appears on the page, so we can still space things out as much as we like, just like it had been when it was fixed before one of the recent updates. Without the fix, we could not remove the spaces within the editor because they were essentially invisible.
Obviously, if everyone creates in the advanced editor like you said, it should be fine, and probably also for those just buying version 6, who did not have to work around the lack of certain formatting when in version 5 from a year ago.