Really?! That's very odd. I have always been asked what kind of stamps I want, whether in Maryland, Wisconsin, California, here in Arizona, and so on. My point remains as I stated early on; those places that don't ask seem to me to be isolated, not the rule.
You are probably right. I think they just don't take the time to ask you. But I didn't know you could get which ones you want. They always give me the ones with the flags on them.