Sometimes, in doing some searches on the NW site, I've come across it offering me a PHX-DTW leg as PHX-DTW-ATL-DTW. It's only been less than $10 more (for PFCs, I imagine) and about 6-7 hours' time and would be worth an extra 1,200 or so base miles. I checked for later in the year recently, and that didn't show up, though.