According to my U-Verse Realtime line stats, the 3801HGV routers that are currently out in the field may be in the process of getting a firmware update.
The previous version of 3801HGV firmware, 184.108.40.206, looks like it is being updated to 220.127.116.11, which matches the newest firmware available in the iNIDs.
I have been seeing this trend for the last 2 weeks or so. I have a new page on the U-Verse Realtime web site that shows the current status of firmware versions that are in the field, it is available here.
One thing I cannot tell from the line stats is how many of these 18.104.22.168 entries are new 3801HGVs that have just been installed, and how many were older ones with 22.214.171.124 that are being updated. So I can't say for sure that AT&T is pushing new firmware to the older units, but there are definitely increasing numbers of 126.96.36.199 firmware in the field.