Mexican food is usually designed to be complemented by different peppers, but a lot of American foods are modified from European traditions, where spicy peppers are rarer. So, spiciness itself is a more unusual taste in our food.
I think that the American culture (especially thinking about the Midwest) has the idea of "spicy vs not spicy", but not the idea of which flavor of pepper goes well with which kind of food. A lot of restaurants here will have black pepper and Tabasco sauce, but not much else, despite the fact that the vinegar in Tabasco will destroy the flavor of a lot of foods.
There's a culture of "spicy and mild", but not a culture of "spicy, but subtly flavored". Of course, I can always go to a Mexican restaurant and find a salsa that matches my food well. But even there, there are usually "mild", "medium", and "hot" labels on almost everything, rather than telling you what kind of peppers were used in preparing the sauce.
