Copyright in an artist's "style"?

The Seattle Post-Intelligencer carries this interesting report of an infringement lawsuit brought by artist Dale Chihuly against two artists, including one who is apparently a former studio assistant. Since at this stage the judge reportedly ordered Chihuly to specify which particular works he's claiming were infringed, it would seem the case really involves the difficult question of the extent to which copyright law protects an artist's style (that is, the claim that the defendants' works look too much like Chihulys as a group rather than this or that particular Chihuly). The leading case is probably the 1987 Southern District case Steinberg v. Columbia Pictures, in which the artist Saul Steinberg successfully sued over a poster the studio had designed to advertise the film Moscow on the Hudson. In that case, the court noted that "style is one ingredient of 'expression'" and seemed to place a great deal of weight on the fact that the poster "was executed in the sketchy, whimsical style that has become one of Steinberg's hallmarks."