Um... maybe this is a Limey thing, but how is eating hamburgers a punishment?
I think the point is that these guys are all spoilt and only eat posh food that costs a fortune, and the one guy, who wasnt even paying for it, decided to complain.
So the boss, who grew up working class, was punishing them by feeding them the food of the lower classes.
The fact that you do not see hamburgers as punishment is the point he is trying to make, that working class people like you or I cannot afford to have such overly high standards, and appreciate things for what they are, and are not stuck up freeloaders.