This is a little deceiving. The rule is not because you are traveling together with your wife, it is because she is on the same PNR/record that you are on. If you were booked on separate PNR's she would NOT get the same allowance as you. I don't have the time to look up the documentation but it is probably online where TTU told you it is and I know NW Scoop posted this on an earlier thread.

John