How much does weight really affect the operation cost?
A couple of old references behind paywalls estimate commercial aircraft weight reduction is worth $300-800/lb over the life of the aircraft, and it is heavily fuel price dependent. This was back when fuel was half the cost it is today, so double it.

Your reference quotes a Northwest Airlines manager who may have been describing savings across their whole fleet of 320 planes. This drops the annual savings to 50/lb/aircraft, or $1500/lb across the 30yr life of an aircraft, roughly equivalent to my two sources.