Necessary? Maybe - maybe not - however, there are things in the update for every device that is capable of running iOS6 - addressing security issues and various bug fixes that are not individually identified.
Is it "necessary"? I doubt it. There are still 4S users running iOS 5, 5.0.1 & 5.1.1 and are quite satisfied. I do, however, agree with Keith that updating to the latest version is recommended.
As I always said over on the CB Forums - There is a reason for the updates. There might also be something "under the hood" that may make your device run a little better. Bug fixes, OS tweaks and the like are desirable. I wold think that would be considered "necessary"
So...even though the hype around an iOS update may not specify anything for your specific device... there may be something in it for you - so just update.
Well I agree with Keith also as well as JMD and one last thing, If they did not have it as much complaining as most everyone did about ALL the bugs everyone found by updating if Apple did not come out with a bug fix ALL of you would be blasting Apple for not doing anything. Now the OP wants to know if it was needed.
For those of us who work with Exchange calendars or with Google calendars over Exchange ActiveSync, the upgrade fixed a show-stopping bug in 6.0 that prevented meeting invitations from being transmitted.