Yeah, I agree that people definitely interpret it wrong, or however they see fit.
I still offer help/hold doors/etc even if I know most of them won't appreciate it and wouldn't do the same for me. Every once in a while, you find someone that DOES appreciate it, and it makes it worth it.
Also, I've had the whole "be polite and do things for other people" thing forced into me for years. I used to get totally bitched out if I didn't properly address someone I called on the phone "Hello Mrs/Mr. so and so, this is Courtney, may I please speak with so and so? Thank you."
it's actually a sad state of affairs, I don't even think about what I say half the time, it's just an automatic response (i.e. if someone asks how I am, regardless of how I really am I respond "oh, I'm fine thanks, how are you?" when they were probably just saying something in passing as a variation on just "hi" and they probably don't care how I am)