Do characters perform Upkeep actions, such as rolls for Blessed/Cursed, during a final battle?
This is clarified/fixed in the FAQ in the Dunwich Horror rules:

Battling the Ancient One
Q: In combat with Ancient Ones, do investigators get a full Upkeep Phase, or is the Upkeep Phase limited in some way during the final battle?
A: Investigators get a full Upkeep phase.

So yes, you roll for blessings and curses.
I can only assume they wrote the original rules the way they did because it's not a normal turn - it's combat, and you don't have any normal turn phases. (No movement, no encounters, no mythos.) So they were perhaps thinking it wasn't actually an upkeep phase, and you simply do everything you would do if it were an upkeep phase. And then for some reason they tried to list the things you do in the upkeep phase instead of just saying &quot;everything&quot;. Obviously that was pretty misleading!