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
Yes, her verbiage was indeed misleading and I also know that you are correct if we were on different PNRs, as in that case we would not be considered to be "traveling together" in this context. (I have, however, been able to get companion upgrades for my wife when we've been on separate PNRs, but only by bringing it to GAs' attention, as opposed to through the automatic system.)