Forget the conflicting info. - this is just one reason I would never travel by air without my passport. Even if the info. that you don't need one is correct, find the officer that believes otherwise (i.e., if you get sent to secondary), and its doubtful that you'll be able to convince them otherwise).
And that's only if you can get to them - IME, its YMMV whether the check-in counter will let you check in without your actual passport - there are threads where folks have been denied. And given airline rules on documents can differ from what customs/immigration rules are, you may have no recourse to argue if they require a passport for check in on a transborder flight. Though its been a while since I've tried using it, I've had AC check-in folks not allow it when I've just handed them my Nexus in the past.