Just agreeing with the folks who say tail load is real and increases actual wing loading.

Tail load IS considered in designing structures and in computing performance and stability data. It seems a small factor in level flight, but if you consider the additional load the wing has to support due to tail down-force, at the most forward CG, and at the limit load factor (worst case), it can be significant to the structure, even for a model.

However, designers of model planes have little control over what the actual tail load of a given model is going to be, since they don't know the exact finished weight and CG that the end user will impose on it. So it's just easier to design for some worst case and specify simple wing area on the kit box. Imagine the confusion at the hobby shop if tail down-load information was printed on kit boxes! Full-scale airplane manuals normally don't even include such information.