Madison to Denver $649 for Return Tickets

I got an email from Northwest Airlines with a table of sample air fares as shown on the left. It shows a sample fare from Madison to Denver for about $122 each way, which totals up to about $244 per round trip ticket. However, when I went to NWA.com to check out the price, it's $649 per round trip ticket.That's more than double of the advertisd price!
Inaccurate pricing. Sample air fares suck.

Then I tried searching for Chicago-Denver, and it came out to $460 per round trip ticket. Catching a bus to Chicago from Madison costs about $35.