Is the question about locomotives or about railroads?
IMHO, a "real locomotive" is a locomotive which adds, or is retired from adding, value to the work of a "real railroad". A "real railroad" is a railroad which transports goods to someplace where they are needed or persons to someplace where they want to be. Of course, by that definition, even the railroads at places such as Greenfield Village and Disneyland are "real", because they (along with antique autos, horse-drawn carriages, etc) are listed in brochures as means of traveling from one part of the part to another without walking.
Sumpter Valley and WW&F are both the results of efforts to resurrect "real railroads" to inform a new generation about the past. The organization which operates the WW&F is even the continuation of the actual corporation which originally built the railroad.