I could see moddability as a separate thing if it was in terms of looking for it in a game because you like to mod games.
But people buying a game, for me, the credit does go to the maker for providing that capability. You have to buy the game to get to the mod.
In terms of people making a bad game, both deserve praise, the developers for making a game which was moddable and the modders for making the game good. There must have been something in the game the makers made to make it worth the trouble for the modders to make a good game of it. I'm not trying to take away from the accomplishments of modders, but we shouldn't take away the credit the makers deserve for providing that platform.