There have been quite a few threads about this. My own experience was a fare of $1,046 BOS-SIN on NW I found on Expedia a couple of years back. The best AA, my preferred airline, could do was $4,100. The best NW itself could do, either on the Web or by phone call when given the exact itinerary, was over $3,000. By the time I got back to Expedia to book the ticket it had gone to $1,246, but I took it anyway.

Anyone who looks for logic in air fare pricing is in for a long day.