Gas furnace valves are easier to replace than electric furnace valves because an electric furnace does not actually have valves. A thermostat, which limits the amount of electricity used, operates an electric furnace. The higher the temperature is set on the thermostat, the more electricity will be used.
A gas furnace needs a valve to control the size of the pilot flame. Consequently, the pilot light controls the amount of gas used at any given time. Another way to look at the question is that an electric furnace valve is easier to replace because no replacement is required, even if replacing a gas furnace valve is not a particularly difficult task.