Yes, this was within 24 hours of departure, so he should have had a seat assigned (mine was anyway). It really seems fishy that they refused to assign even a boarding zone until I paid for a seat, then magically it worked.

Now, honestly, I was gaming a bit - just see if they separated us and pay for one of us to move at check-in if needed, which seemed lower chance given how empty the flight should be. Even in that case, it's only $10, and would have been $8 had we both paid for seats in advance.
On our return I did select seats - figured a Sunday afternoon flight will be pretty full.