I wonder if there is more informal chit chat in business or first class. Maybe people assume that if they some how had the money to buy a more expensive ticket or had the skills to get an upgrade then the person would be OK.

After reading all the replies so far I assume that the general feeling is that if you are friendly to your seat mate, then he/she will turn out to be a chatter box or a psycho and it will turn out to be a terrible flight. Has our world got that bad?