When going to my work in the Netherlands by bus, I always thank the busdriver when I get out. A colleague of mine was riding the same bus once, and he was very surprised I did this. He asked me why I did that and seemed to have a hard time understanding why somebody would. For me, it is just a gesture of friendliness.
I was in the United States this summer and my sister (who lives there now) pointed out that people on the bus would ALWAYS take the front exit so they can say goodbye of thank you to the busdriver. This is very inefficient since all the people getting on the bus have to wait until all these micro-conversations are over, but it does embody the friendliness I experienced almost everywhere in the United States, as opposed to the Netherlands. If I could choose, I think I will be happier with this friendly, though less efficient way of interaction in a bus.