Being someone who always rents a car-- I find this whole topic fascinating.
I've never waited in line for the busses, so if I walked up to the bus stop and there were people sitting on the benches but they made no move to get ahead of me when they saw me coming, I'd assume they were there for the bus, but possibly not interested in being first ????
If they didn't move until the bus showed up, I'd ask them if they'd like to go ahead of me, since they were there before me, but it sounds like the whole bus etiquette thing is scary and just reading about it stresses me out, so it makes me glad I rent a car.