I wonder how much of that is real attitude and issues, and how much is joking and ribbing read wrong.
I do agree that APS is probably one of the nicest places online, in terms of polite behavior, especially considering the topics under discussion. I also like the fact that the behavior is more self-inposed by the participants then forced by the moderators. It allows for much more freedom of expression and it keeps it feeling like a conversation among adults.
We may not all like each other, but we (mostly) respect each other.
I also really like that while you and another poster may be vehnimently opposed to each other in one thread, you can cut up and joke around with each other in another. There are very few grudges held between posters and there has always been the attitude of disagreeing on a specific opinion rather then just hating on everyone that disagrees with you forever and ever.