As a sociologist, the question about income levels struck me as pretty innocuous--it's the sort of thing you always ask about on surveys, along with gender, race, etc. (Actually, it's odd the survey didn't ask about race.) Sociologists doing survey research sometimes have to wrestle with how to get people to answer probing questions about controversial political topics, drug use and sexual habits. Income levels are pretty tame compared to that. And income could be relevant to the survey--correlations between that and how much money someone spends on games, how much time they spend gaming, etc. could be interesting.