I work in an European ARTCC. For us it's not compulsory to ask the remaining fuel in time, as far as I know. It's probably a silly question, but I wonder why US ATC must ask this question when an aircraft declares an emergency. What really matters for me are pilots intentions... But I probably miss something here, there must be a reason.
When it comes to fire fighters requiring fuel remaining in kg / pounds, I wonder how they deal with it... I recently had a "pan-pan" (possible tyre burst), and the fire fighters wanted to know the "remaining fuel in kg"... The thing is, the aircraft was still 30 minutes from landing! Did it help the fire fighters to know that at this point of the flight he had 4600kg of fuel remaining? Because by the time he lands, the fuel left in the tanks will be a lot different...