For reasons that we cannot begin to imagine, known hacker and security guru Stefan Esser (i0n1c) has tweeted that he will do an untethered jailbreak for iOS 4.3.5. Yeah, not iOS 5, but iOS 4.3.5. We don't get it, either.
Dedicated jailbreakers that haven't wanted to ditch their untethered jailbreaks are likely still on iOS 4.3.3 (it was the last firmware that was accompanied with an untether, ala JailbreakMe). Then there's the possibility of a few users who truly hate iOS 5 and haven't updated for that reason. Whatever the intention, i0n1c seems to think that we need an untether for 4.3.5.