Exactly, you prove my point. In America at least the clown has been so reduced to simply the circus archetype that there is no longer any room for other kinds of clowns, and it is the circus archetype which we see transformed into the 'scary' clown. Not the court jester or the harlequin or, as you mentioned, the Pierrot.
Back in the day, Red Skelton did a hobo-clown act, and if we go further back, Charlie Chaplin was in a similar vein, but comedy today is taken in the form of the sitcom, not the Punch and Judy show. (I doubt most Americans today could even identify a Punch and Judy show.)
Don't take me wrong, I'm not trying to rag on Americans. I don't know enough about foreign countries to speak about the state of clowns in Britain or Mexico. (Although I was rather disappointed to find out that the British magazine 'Punch" had nothing to do with the play.)
Have you read the Neil Gaiman Punch and Judy book ("The Tragical Comedy or Comical Tragedy of Mr. Punch: A Romance,") or his Harelequin one? I liked the Punch and Judy, though I haven't read the Harlequin. Of course, even here we can see the clowns transformed into horror, although Gaiman's horror isn't the same horror of the chainsaw weilding clown...
I think if we had more clown variety, more sad clowns, more ploty clowns, we wouldn't see as much of the movement towards 'clowns are scary,' though.