According to this article (»
www.h-online.com/securit ··· 849.html ), there were more than 160 security issues that were recently fixed in the Windows version of iTunes, but many/most of them had been repaired on Mac OS X in July by the release of Safari 6.
So, if I read this correctly, these 160+ security issues still exist on Macs which do not have Safari 6 installed. The articles says that these vulnerabilities affect HTML-based pages that are displayed in iTunes, but it is conceivable that other web pages (on other sites) are also affected.