Beer and Identification

So my wife and I are in Walmart this afternoon and I was purchasing a twelve pack of beer among other things. My wife was waiting at the end of the checkout counter where the plastic bag carousel is to put the bagged items into our cart. The lady at the checkout notices her when she scans the beer and asks for my wife's identification. I say that's unusual since I'm the one buying the beer. She says she still needs to check my wife's ID. WTF is up with that? If my kids or friends were with us would they ask for their IDs also? If I had also decided to buy cigarettes would they do the same thing? I felt like arguing the point with her but as usual there was a long line and I didn't want to upset the nice folks behind me. But again I ask WTF??