The Queen is an ugly old tart. If it were up to me, she would be dragged out of her palace and beheaded in front of her family.....Just before they get shot themselves.
My point is, that while Clarkson's comment was not serious and should not be taken seriously, it wasn't particularly funny either, just like the above post. Humour, when done properly has other elements designed to make the listener think a little before the penny drops. Of course, it is clearly easy to make a right winger laugh, just make a death threat, they find them funny.
I like Clarkson, and don't care about his politics. He is funny on his show, but this was not really comedy now, was it?