i definitely see where you are coming from, DoH, but i think it all comes down to your definition of "preference" internally. To me preference describes a system of ranking and judging. While this can change, it does not change on whims. Someone who says "i prefer ketchup" will actually choose ketchup 99% of the time and will only not choose it in rare cases when they want to branch out or are feeling adventurous. Similarly, someone who says I prefer blondes is just more attracted to blondes. They don't choose blondes for any logical reason, its just their tastes. I agree that sexual preference may be too weak of a term, but i think when describing the things you like its perfectly acceptable. "I prefer fair skin" gets the point across finely.
I hope i didn't lose track of this convo, thats where it all started right?