I ran my test on XenForo. It might have to do with many of the other add-ons on your site possibly adding non-Javascript code before the closing body tag, after VaultWiki has already deferred the Javascript to that place.
As I described in my first reply above, VaultWiki already does everything Google Pagespeed is suggesting for you. In Chrome, visit this URL:
view-source:http://stratics.com/ams/stratics-calendar-guide.101/
Scroll to the very bottom, and you will see what I mean. If you can think of a way to move this even further down, I'd be glad to hear the explanation. The scripts you see there cannot actually be deferred themselves, because they are the ones that do the deferring for about 6 other scripts listed there, plus dozens more you can't even see.