IP:

Just a couple of other thoughts. Have you looked into NW's contract of carriage or the rules for the fare that you purchased? If your fare in fact allows standby for later flights on the day of travel (which several knowledgeable sources here have said it does), this must be written somewhere in the rules or contract of carriage, right?? If you could point to some rule in your dealings with NW, it might clear up the problem.

Also, I hope you are planning to contact your credit card issuer to dispute the $100 charge.