I guess it might be a cultural context, when you watch for example this week a tournament in Rotterdam (the most important tournament in the Netherlands) you actually don't notice a change in behavior of the crowd as it supports players when one of them is a Dutchman and the other a foreigner, it's all the time the same, well, it may be one of the reasons that Dutch players suck at home tournament...
I think it's great that the crowd in Sao Paulo is much more enthusiastic than at Costa do Sauipe but constant cheering service faults of the opponent and his easiest mistake are rather tasteless from many parts of the world.
Well, there is a cultural context, for a long time Brazilian culturally invested much of their pride in Sports, because didn't have much else to look at, that's why had figures like Ayrton Senna and the passion for the Football team. Brazilian deposited patriotic passion in sports, more than in politics, Military like the US or other things, than many other countries do, I agree.
But if you look at it, Brazil is one of the most peacuful nations ever, having pratically never been to an actual war, so sports I think is almost like a scape valve, to evoke the strongest passions and can go to "war" figuretavely.
I don't like it some parts of it. I was in the crowd today can;t deny it was great fun at times, it was just a perfect storm, the best Brazilian tennis player currently against an unkown Argentine player, stalling between and taking long time between serves and Bellucci on the come back, it really got to the crowd.