Good catch on the IP addresses being the same for the two URL's (res.nwa.com and flynwa.expedia.com). Still doesn't explain why one can show me BRU-SEA availability and the other one cannot.

I agree with the other poster that NWA.com offers more flexibility than many airlines websites (UA comes to mind)...but it's fundamental for their website to be successful to produce search results between city pairs that they actually serve and that valid routing exists. That is above all, the #1 function of an airline website. Freq flyer info, etc. is just a nicety compared to being able to buy a ticket.

-RM