As a ex-NWPM and now DM, I have to say,
Regardless wherever they are sitting, even its in the back, coach middle seat, next to the crying baby, or the worst - all together,
chances are PMs and DMs will fly Delta again.
NW wasn't giving their WBC away just for the cause. and DL is doing the same. Like the MOST other airlines does around the world.
(especially SQ, KE agents gives you worst look i've ever seen in my life if you ask for the "Free" upgrade.)
Back to the Principal, You get what you paid for.