You don't understand what differences in etiquette are. You have to have some flexibility, your way isn't the right way, it's just one way. I'm also from Wisconsin, people here are crazy nice, it isn't like that outside of the midwest in my experience (actually I just saw a comedian over the weekend who was making fun of how friendly people are in the midwest compared to the east coast "you guys are so nice,... we think you're ****ing with us."). And, even though I used a brazen word like "nice," I hope my meaning is clear. People outside this region aren't "not nice," they just have different strokes. Learn to read into intentions, and to keep an open mind, it will help you interact with different kinds of people. If something appears to have been rude, think about it, did they mean to be rude or is it just different? If so, is it passable? If not, then you can have grounds for saying something, if it's just not something you are used to and not the end of the world, maybe it's understood by you that what they did isn't against their etiquette, then you can find resolution in not deciding not get upset about it.
You are talking about just small differences in etiquette in the same country, imagine how bombarded you would be if you went to like China. Open your mind, it's more than just a theoretical idea, as you are finding out, it's harder to be open minded when you are actually confronted with something different. To learn to accept someone else's code of conduct as valid as yours is one meaning of being accepting of "other cultures." It seems a lot of people go around thinking they are open minded but have never been put to the test.
Asking someone "why are you being rude?" isn't a smart way of bringing up something. You automatically put them on the defense.