Based on all the posts, it seems that everyone should travel with earplugs. You never know when you may need them - either for yourself or to offer to a roomie.
For those who have trouble with earplugs, try the polar fleece headbands that go around your head and over your ears. I wear them in the winter and find them so comfortable that I have fallen asleep with them on. They do well insulate against noise. When I am outside talking to people I often have to pull them back off my ears so I can hear.
B needed to speak to A first. But that doesn't mean that A would have had to pay for half the room, even if A knew about the snoring. Even if they had discussed it, that wouldn't guarantee they would have thought of the ear plugs.
Organizers of such trips should recommend on the brochures/flyers that everyone bring earplugs.
My mother was a VERY loud snorer. When we traveled, we kids would fight over who would room with her. When I was rooming with her, I'd shout "Quiet!' and she stopped. It never occurred to me that she probably knew I was doing that as she never mentioned it. Oddly, that was probably fair, we were both getting woken up at the same time!
Some years ago, a friend and I went on a trip together. She was clearly angry the next morning. I had no idea what was up with her and didn't ask out of respect that she had a private issue she didn't want to confine in me and to give her time in general. At some point, I realized she was mad at me but I couldn't figure out why. I wouldn't play her passive-aggressive game and ask her. It was an awful weekend.
Some time after that, someone else told me I snored. That was probably what she was angry about. But the damage had been done. We weren't really friends after that. Just acquaintances in the same circle of friends.