I am as straight as they come. And for someone that is very straight, and very uneducated about gays, I think the question arises from 'what you know'.
In a typical straight relationship, the female normally has a duty as the wife, and as the male, we normally have a duty. This is just the way we've been brought up. My wife doesn't expect me to clean the house or kitchen, but she does expect me to take charge of finances and make sure there is a food on the table and a roof over our heads. I expect her to be in charge of the kids, but don't expect her to fix things around the house or carry the heavy stuff around.
Straight people tend to think these roles should exist in any relationship, where it's gay or lesbian.
So what they are basically asking you is - who makes the bed and who changes the bulb / plugs?