It is because the A5 devices untehered JB takes a developer account in order to place the untethering files, without it, there is no chance. At least for now.
As he has promised via his Twitter that A5 untethered jailbreak will be released in a week. I believe he meant it with his words. Especially he had recommended to people with iPhone 4s in hand to upgrade to iOS 5.0.1 firmware.
So be patient and wait guys, good things come to those who wait and patient. You can read his entire A5 FAQ post from this link.