I think it used to be there in past versions, Roy. I’ve heard of a “missing” piece on this menu before.
If you look at the very bottom of the misc screen, you’ll see the following:
_________ .
The line is actually the top edge of an adjustment box, and the dot is the end of the upper tip of an adjustment arrow. Similar boxes/arrows are seen just above on the “rotation speed” and “translations speed” settings.
So to answer Rampage’s question, it’s an “oops”. The preference editor has fixed size pages throughout, and the misc page has more options than can fit on that sized page. The programmers forgot to adjust the menu page size to be long enough to include all the options on all the pages (or to include a scrolling function). 
I’ve sometimes wondered if there’s only 1 item covered up there or if there’s a dozen more adjustments underneath it that we’ll never see! 