This weekend me and my buddies let a hundred-and-then-some people hold and handle our swords.
I noticed that those who have a natural feel for it, i.e. instinctively hold the sword in the correct manner, are usually the ones who say it's lighter than expected.
Many of those people were (some very young) children so it's obvious that physical strength isn't a factor.

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I have another point to add to what Michael F. wrote. Earlier in the 20th century, most of the sword fighting seen in movies about the Middle Ages involved cuts with fast wrist movements which are more consistent with sport fencing than with historic European martial arts. These sort of movements do not work well with swords with any substantial mass; consequently, trying to perform these techniques with any sort of sword, be it wall hanger and or historic replica, will probably result in the person thinking that the swords feel heavy. Even if the individual does not actually try to perform these wrist movements, the very fact that the sword feels too heavy in hand to accomodate to such movements will probably lead the individual to think that the sword is heavy. While this sort of "sword fighting" is no longer seen in films today, it did influence more than one older generation, whose views no doubt served to inform younger generations to a certain extent on the subject. Also, groups like the SCA still typically use quick wrist movements with their padded swords which don't work with real ones, so this phenomena still exists today and still probably informs, to an extent, modern people's views on the subject.