我的理解是:The Parthenon is larger than usual可能理解比的是The Parthenon和usual Parthenon在大小程度的不同,从句义理解明显不合逻辑,The Parthenon是独有的东西不存在usual。实际比的是The Parthenon 和 what is usual for a Doric temple(也就是其他通常的Doric temple).
另外一个例子:A grasshopper 和A usual grasshopper for a member of the insect class比大小,明显感觉不合逻辑,应该是A grasshopper 比what is usual for a member of the insect class(也就是通常的昆虫)大,分号后做了解释。