I don't find it surprising at all that most people assume relationships to be exclusive. After all the vast majority of relationships are, and more importantly, the "standard" image in our society is one of exclusive relationships. I found it more surprising that most people assumed that A+B and C+D are indeed couples, because their behaviour doesn't necessarily suggest that.
Not surprising nobody fell for the "rich is bad" trap, that was obvious, but Dan doesn't do anything that can be judged morally, except if you assume being rich is a very bad thing in itself.
Also surprising people viewed Gary so favourably, he only passively helped Fernando, nobody concluded he just didn't care.
Most people viewed Fernando as a poor guy, nobody thought he could be hungry for other reasons, like I jokingly suggested, it might be his own fault.
In a society that values honour more than ours (more of a macho kind of honour), Edward might be judged more favourably, nobody assumed he was defending Betty's or his own honour.
In conclusion, most people seem to have a rather idealisticly positive view of humanity. Most people see economic conditions as unlikely to change. People have a conservative view on relationships on the one hand, but don't see them as ultimately that stable either (because nobody thought how bad it might be for Dan to get walked out on and nobody questioned Adam making a move on Carrie.)