Commercial attribute for improvements

[Kloreep]

I wanted to make marketplaces and banks cheaper for commercial civs, but, when I went into the editor to create a .bic with markets and banks with the commercial attribute, they already had that attribute! To be sure, I unchecked the commercial attributes, saved the "scenario", checked them back on, set the human player to start in the middle ages, and saved again. I started the scenario as the Indians, but the marketplace still cost 100 shields.

Is the commercial attribute hardcoded to not cheapen the cost of buildings?