I'm not sure I understand here...so please feel free to provide clarification if I'm wandering away from the facts.
You say you used your wife's account to buy a gun for yourself.
Let's leave aside the whole FFL transfer thing on your end, where you pick the gun up. Was there any way for Bud's (the agency selling the gun) to know that the person buying the gun was NOT her?
If not, then the gun that they were selling was NOT going to the person they believed it to be going. How, then, is this NOT as straw purchase in the eyes of the law?
The way the law is written, Uncle Same does not care that you are legally able to buy a gun when it comes to a straw purchase. It cares that the person buying the gun is the actual recipient of the gun.
Most people focus on Form 4473, which is where it's documented as to who the gun is going to and where lying on that form would be the violation that straw purchases makes. However, if Bud's believed they were selling the gun to your wife and the gun instead went to you...I can see where there may be a problem.
Let's change this a little bit:
You go into a store, your wife wants a gun. She picks out a gun, you pay for it, she fills out the 4473 in her name and the two of you walk out happy clams. She got the gun she wanted, right? She filled out the paperwork in her name and the gun is legally hers, right?
But the reality is that the way in which this sale took place makes it a straw purchase. YOU purchased the gun because YOU paid for it and SHE took possession of it.
It seems to me that it's pretty clear that the purpose of the law is to ensure that the person taking possession of the firearm is the legal owner. However, the way it's written doesn't work out that with respect to straw purchases...like it or not, agree with it or not, that's the way it is.
So, I don't see where your particular situation is legally any different than the example I provided. Bud's believed your wife to be the recipient because you went through her account. The fact that you are her husband and are legally able to own a gun makes no difference.