I just went thru this w/ NW. RDU/DCA on NW lists:

$112.50
MIN STAY - RETURN AFTER 1 DAY AFTER
DEPARTURE FROM ORIGIN
TRANSFERS - 8 ONLINE PERMITTED OUTBOUND 4 INBOUND 4
[...]
ROUTING 206 FROM-TO RDU-NW-EWR/NYC-NW-DTT/CLE-NW-
BHM/BNA/CHI/EVV/IND/LEX/MKC/MKE/SDF/
STL/TYS-NW-MEM/HOU-NW-WAS*
FROM-TO RDU-NW-HOU/MEM-NW-TYS/STL/SDF/
MKE/MKC/LEX/IND/EVV/CHI/BNA/BHM-NW-CLE/
DTT-NW-NYC/EWR-NW-WAS*

I cannot find a single engine (ITN, travelocity, nwa.com, expedia, orbitz, etc)that: 1) offers IAH as a connection or 2) will price the RDU/IAH/DCA segments as anything other than point-to-point

Yet, when I called a NW CSR she was able to route it for me just fine at the proper price... however, she got quite frustrated with me when I started the "what about RDU/IAH/ORD/DCA..." stuff... I was told that ORD is not a "transfer city", I said "I know, but can't you put me thru MEM? and create RDU/IAH/MEM/ORD/EWR/DCA? that appears to be 4 transfers and a 'legal routing'"... there was just this "sigh... and some mumbling that I should just look at the website or something"... I just hung-up...

so given that there aren't many engines that can book this wild stuff, I guess that it is common for everyone here to drive the CSRs crazy like I just did... is that accurate?

PS even if what I suggested was not a legal routing, she was still really turned off at the idea of even researching it for me