But why would you update? iOS6 adds nothing of value.
The latest iOS 5 is full of known holes. Hundreds according to Apple's security release notes.
http://support.apple.com/kb/HT5503
If you want people to be able to simply break into your phone by luring you to a specific website or by sending you a specially prepared PDF or image, suit yourself. There are also known ways to steal you iTunes account information and go shopping with it.
I'd call this more than enough value.
Why do you think Android is so vulnerable to Trojans? It's not just the possibility to install untested apps. It's also caused by millions of phones running old Android versions full of security holes.