Horror movies have never had massive budgets for their advertising campaigns, hampered by placement issues due to the age rating. Instead they rely on their trailers to create an atmosphere that can scare within a short 1 minute clip.
Freddy vs Jason could have been a great comic book style dark film but instead they went down the route of parody. Instead of getting the most scary aspects of their individual characters they instead made this slash fest more of a comedy feature and this began well before anyone ever saw the movie. An advertising stunt like a weigh in might have been great PR if you were promoting characters that could perhaps both talk. Getting the legend Michael Buffer to announce the two was an expensive task no doubt.
Did it work? I personally don't think so and having seen the film I found it wholly disappointing.