Do people here from outside the US think this is the case everywhere? Because I'm from Latin America (more specifically Brazil) and I don't think ignoring the lower paid staff is the status quo. Actually it is considered pretty rude not to at least acknowledge them and say the usual pleasantries (Good Morning, Hey Jon!, etc...).

Having been to the US I'd say I don't think that is a fact everywhere also. In NYC for sure, as people are more transactional with each other, or SV where people are awfully superficial/shallow. But I've been to cities where people are much warmer (from the top of my head, San Diego).

One step further I'd recommend you to do is to sometimes move past from the "automatic pleasantries". For example, when the cashier at the fast food asks you "hello, how are you sir", instead of answering "fine, thanks, I want...." go for "I'm good Jennifer, and you? How are you doing today?". My experience is that this always get people off guard and has a very positive impact of them, as bring them back to a more human (and less transactional) aspect of the interaction.