I think they operate so differently because the deisgners viewed it as an assassination tool. Concealed until the last moment and silent.
Thing is, you could also conceal a pistol (heroic scale doesn't help that argument though
) so it probably should follow the same system as crossbow pistols.
I think if I ever do a Witch Hunter warband, I'm going to arm my captain with a brace of crossbow pistols for fun. Ludicrously expensive but the model would look cool.