The regulation around replica or imitation firearms cover this, the exact wording escapes me but it's something like:
"resembling or could easily be mistaken for a real gun"
...which I suppose the PR satisfies, in a dark ally if your victim is Mr McGoo, but they have to appeal to the lowest common denominator so in it goes to the same bucket they classify accurate gun replicas (or disabled real guns), flick knifes and other prohibited weapons.
The irony is of course that the Pulse Rifle poses no real threat other than as a bludgeoning weapon, which my wife would no doubt restort to if I considered converting one of the rooms in our house to level 3 secure storage.
We have sort of have the same law in Canada about replica firearms and it still went through.