Typically the word scale is used to mean several things.

Scale = Warbird type planes (looks and shape and size)
Scale = size and shape
Scale = size, shape and weight

Size is also relative, just ask your girlfriend/wife...ooopppsss wrong subject [&:]

Anyway, lets take a scale sized Ultimate 10-300 as an example. The real thing is very small. So to have a "scale" sized Ultimate 10-300 like Wildhare, Hangar9 and Goldberg make, the plane is going to be relatively small compared to an Extra 330 or 300 or the Sukhoi, Edge and others.

Also, planes that have shrunk down in scale to fly well for R/C most likely have had changes done like more rudder, bigger ailerons, longer fuselage so as such they are not "true scale". The big thing is 3D and allot of planes cannot do 3D without "enhancements" to the rudder, ailerons and elevators.

Like Exter said, the wallet has tons to do with it. Just look at what some guys are doing over in the UK. Scale size 747's A380 Airbus, DC-10, L-1011, B-52's and on and on.