DISCLAIMER: All opinons expressed, by this writer/poster, so far on this thread or on any other thread in this forum do not constitute nor are they intended to imply legal opinons. These are simply my personal opinions!
I guess my previous post regarding Affidavit of Support could make do with additional clarification. Personally, I do not think there's any need for an Affidavit of Support if the Principal Applicant undergoing a DV AOS process is on a H1 visa (for instance) and, of course, is currently earning an income. I very much doubt the IO will insist on it before approving the application (even if the interview letter requests for one and the principal applicant shows up without it).
However, if the Principal Applicant is on a H4 (for instance) or some other type of visa that prohibits the principal applicant from working, and the spouse who is also adjusting status as a derivative of the principal applicant is on a H1 visa, then the spouse can sign the Affidavit of Spouse since the spouse has been acting as the head of the household already for tax purposes. At the end of the day, the IO may not even request for the Affidavit to be submitted they show up for the interview, this however is a viable solution to couples who may be in this situation and do not want to involve some external party in their immigration process.
Again, these are simply my personal opinions, they do not constitute legal opinions and I do not work for USCIC, hence I'm not claiming a definitive knowledge of the internal workings of USCIC.