This is the main site for XenForo, to which they all (meaning forum software creators) use their latest product on their site (with some minor edits ) to show it off.It might Andy, so there is another reason !!
I hardly know anyone that reads the footer besides to find out what software the forum is using. Currently, anyone who skims over the title of each section can tell what the latest version is.
I think that showing it in the footer is just another security issue, after all if you tell me (or broadcast it) what version of (for example) Adobe Reader you are running, you can expect people sending you a few hundred *.PDF files that contains an exploit just for that specific version. Why make it easier for people who want to harm your site? Also, if you don't have the latest software and people know it, with there being nothing seriously wrong with it (performance or security), wouldn't that make your site look like it doesn't have competent administrators?