Ambulances and Fire Trucks

When someone calls an ambulance, the trend is to send along a fire truck (in the US anyway). Other than to relieve the tedium of waiting for a fire to break out, what is the reason?

Obviously, there is an epidemic of spontaneous human combustion.

'cause firemen are trained in emergency medical assistance and usually can arrive quicker than an ambulance.

Fun possibly true factoid: In Virginia, or certain parts thereof, the phenomenon is particularly egregious because funding is partially determined by whichever orginization shows up on the scenes of accidents first.