Ignoring minority while generalizing about a group, any theoretical reference?
I think the exceptions are implied. If someone says, "All Russians like vodka" then we understand that there are no exceptions to the rule. People get frustrated when you're overly specific about the percent of Russians who like vodka. Instead it's safer to just say Russians like vodka. And bears.

Influence: The Psychology of Persuasion talks about why we operate based on generalizations. We would freeze if we analysed all the details of every situation before we act, so we make generalizations.

Thinking, Fast and Slow is an excellent book talking about the latest research in human biases from one of the foremost experts in the field.