Well no. Actually, in my opinion at least, it is a sensible rule.
There have been cases in these forums where a poster has claimed, usually as an honest opinion, that another user has illegally uploaded the work of a content creator. It later turned out that the uploader had permission from the creator or that the creator had included the statement "free to modify and upload" (or similar) in the assets description. In one particular case, where I contacted the original creator, his response was "I don't mind if my work is copied, modified and uploaded".
There was also one case where a "childish spat" between two creators resulted in one falsely claiming that the other had plagiarized his work in an attempt to get the others work deleted from the DLS.
So a claim from another party that an asset has been plagiarized is not enough to prove that it has. N3V has to get the opinion of the original creator. But, as a poster above has noted. this does raise the question of what happens if the original creator is no longer with us?
This is not to say that gramma is innocent - he does have a bad past record on this but for long while now he has payed by the rules.
My thoughts.