I missed my first upgrade in two years last month on MSP-SEA Friday night. Normally that route hasn't been a problem for me. In any case, I had my exit row pre-selected so all was well.

I wonder if this is in part due to higher load factors? Haven't the load factors on NW been on a fairly steady increase? And haven't they been slightly reducing the frequency or volume of available seats? That'd be my guess. If someone wants to be a research hero, they'd go look up the load factors and prove me wrong.