This is the same on all airlines. While the cheapest fare is normally online, the phone reps can not access those fares. What would the point of making it a web fare be then? The problem becomes that you can't change the ticket online and thus be able to use the web fare, instead it has to be repriced into a regular fare. Even NW has problems with this. I've been able to do some changes online in the past with their site, but normally have to call to get it done.