Having done suvey work, it's one of those seemingly ridiculous questions in the "ask everyone" category, like income and religion. Nothing to do with the current survey, but used for a larger database. I always hated them, sometimes I just filled it in randomly without asking.
Thanks, zhoen. I've never been asked that particular question before.
I just assumed it was thrown in because they were trying to figure out whether the folks who read books were the same folks wealthy enough to invest great gobs of money. You know,rather on the order of "how do we target financial services to the right people?".