It does seem that of the two theories re: Chat behaviour, the "I HAVE THE RIGHT FUCKER!" theory is winning.
Two theories are basically thus: The first is that on the Free system (ie: PSN), people won't give a shit because it's free, whereas those that have to pay for it will be mindful they are charged for the service, and could lose it due to abuse. So, for fear of losing something they coughed up for, they behave.
The second theory, which is the one that seems to hold, is that people treat the Free system (PSN) as a sort of 'public domain'. In the same way you wouldn't call a stranger in the park a dog-fucking shitbag, you don't howl abuse at people on PSN. However, since you PAY for Xbox Live, you've bought the right to behave however you want.
Five hours on Halo 3, then five hours on Resistance 2, should clarify which of these theories holds true.