Because of the way vBulletin computes $styleid and doesn't really explain how it got there, VaultWiki doesn't have an easy reference as to what the existing $styleid means. Thus, the value must be recomputed. This is not deprecated code but a workaround to prevent a caching problem involving multi-domain wikis. $vault->misc['styleid'] is actually set in vault/special_class_wiki.php.
However, it is true that this entire condition does not need to be parsed unless $vault->misc['styleid'] actually has a value.
Fixed for the next build.