Many theropod dinosaurs like Tyrannosaurus should have feathers, but it is not yet clear how widespread they are in others. At least some definitely did have scaly skin, and a 2009 commentary I found here (pdf) includes sauropods like this and many other plant eaters among those groups.
In fact you will notice it wasn't clear there were feathers in any dinosaurs besides theropods, it depends on whether you interpret the bristles in Tianyulong and Psittacosaurus as related. That's still largely true. Just this July there was another find, Kulindadromeus, interpreted as better evidence the dinosaurs shared ancestral proto-feathers; it will be interesting to see how well that holds up.
All in all, though, I expect the artist knew what they were doing in leaving them out here.