Yeah, obviously in the 1954 edition he didn't know that; in the 1972 edition, he leaves all the obsolete discussion in and just adds a footnote saying that FIshburn proved boundedness and giving a reference! Had to look that up separately. Didn't notice it either until late in writing this.

Fortunately (since I'm away from university right now) I found a PDF of Fishburn's book online: http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=AD0708563