saying Thanks

Is it rude to not say thank you? I mean, to a complete stranger? To a family member? To a close friend? To your husband?

I feel that saying Thanks TO EVERYONE means many things 1) acknowledgement that something thoughtful happened; 2) that the act/thing was appreciated; 3) shows you are paying attention; 4) that person is doing something thoughtful for a reason, etc...

Am I reading too much into it? Do people just think it's a phrase and dont really think about what is it, or what it means? Do you feel that you dont need to say it because the person knows you so well that; of course they appreciate it? Just curious how others feel..... wondering if I am weird...