I think you might be going a little too deep.
The Imperial Sword is probably just made with better materials.
What do materiels have to do with anything ?! I think you are the one that might be going a little to deep , this is an elder scrolls game and so like all previous ones weapon pricing is done according to the actual weapon stats , same goes for armor .
and since they were completely identical in the visible stats , that means they had to differ in hidden ones , such as reach ( and seeing how the imperial sword is shorter than the steel sword this is very possible), which you can modify in the construction set in oblivion and presumably in the creation kit for skyrim .