Roger:
I don't think that is generally true. The issue is how the Japanese sword is sharpened. It achieves its edge from the polishing of the two sides and not from sharpening the cutting edge itself (as in Western style). So being out of polish along with going in and out of a scabbard for 80 years is probably what makes them dull. That said, some parade swords and others were issued without an edge. In addition, swords issued early on came with sharpening stones, which ended up tearing the edges so were not used for long. This is my understanding, however others may argue differently.
John C.