Some related threads from NW:
http://www.flyertalk.com/forum/Forum35/HTML/006138.html
http://www.flyertalk.com/forum/Forum35/HTML/006720.html
The jist is that NW fliers are not happy that NW was moved from C to D.... the thread points out that C has elite security (for Southwest???) while D does not allow FC/elites into their short security line. The difference in policy is a matter of the "First Class/Elite" line listed on the C concourse sign and not on the D concourse sign.