Traditional American furniture design is characterized by solid wood in natural shades, with upholstery, furnishings and décor to match. This does not necessarily mean that solid wood furniture in its natural color is out, since modern designs can make good use of the natural look of many types of wood, particularly American cherry and birch.
However, if the term 'modern' is associated with pure white furniture on bright red or blue carpeting, or brightly colored pieces sitting on pale-colored floors, then not too many American designers tend to go for that type of contrast. Still, when you think on it deeper, this is not 'modern living room furniture' design we are discussing here, but 'home décor' - and a form of home décor that many believe went out in the 1960s.
So perhaps American furniture designers are correct, although their 'modern' upholstered pieces appear to be traditional designs with brightly colored or white upholstery. Leave American furniture design to the ordinary American, and the results can be awesome - so much so that some of these furniture manufacturers have added their clients' designs to their regular range! If you have some good designs for modern living room furniture for your own home, then you can do the same.