Departing from the US, the old United would never ask for a passport if you check-in online (where you enter your passport number). With the new CO-dominated United (post March 2012) they asked for my passport in the SEA lounge (and stamped my BP) and I think the time before that they asked to see it at the gate.

Departing NRT they asked to see your passport at the gate pre and post March 2012.

BTW, there is a major upshot in going through NRT: you get international service (free meals, beer, wine, and sake, at least on UA) instead of domestic service.

There is not a huge difference in the travel distance between the NRT transit and the HNL transit. HNL is a bit shorter if you are coming from the southern US while NRT is a bit shorter if you are coming from the northern US.

You do not need a passport to transit through NRT to GUM (I have friends stationed overseas who've done it during emergency leave), but you'd be crazy not to have one in case something happened and you need to enter Japan.

Incorrect. You are required to have a passport, period. Military people stationed abroad have IDs that can legally substitute for passports on official orders or whatever else. But civilians are required to have passports.