S3 still does not officially have Jellybean, 4 months into the phone's release. in 5 months or so the S4 will be out. Sad
I'm starting to hear rumblings that Google is going to try and remedy this with something in 4.1.2.....I've read they are going to try and put a pure AOSP version of Android out that each device can run in an Update Center of sorts. Then the particular device manufacturer can later release a version of Android with their custom skin/OS/whatever you want to call it.
I get the impression that Google intends for the user to be able to run the AOSP (if you will) version as soon as it drops from Google to their device. This has been a point of contention for some companies in the past and you will still deal with carrier delays, but at least they are trying to address the issue.