I've heard rumors on both sides of the Chess Piece argument. The one I found the most interesting was an older - much older - gentleman cast member in the MK I met that I struck up a conversation with. Besides telling me how sad he was that he just put his wife into a nursing home because he couldn't take care of her any longer, we talked about several stories from his time working for the Mouse. He's worked there a VERY long time, since '71! One of the stories he told me had to do with this very topic.
He said that while the HM was being built, it was widely known that one of the imaginer designers was fond of chess and kept a chess set on his desk. He said that when they were trying to design the decorative caps for the HM turrets, they kept getting stuck with the idea of pointed tips, but ultimately the design was too traditional gothic looking. They wanted something to lessen some of the gothic overtones of the roofing and the designer's chess set became the inspiration because of the various shapes. Some were rounded, some were more cylindrical in shape and it just fit perfectly with the cartoonish gothic style they were going for. He said that as they were designing the HM, the concept continued to evolve into a more detailed story. He said the only shape they didn't intentionally include for the turret caps in the chess set was the knight. First, it didn't fit into the design and it was too obvious. But more importantly, this was a subtle way for the imagineers to poke back at operations and the entertainment department for "axing" (no pun intended) the entertainer position for the actor who used to roam the hallways in the knight armor at the
Disneyland haunted mansion. The same designers of the Disneyland HM originally intended the knight there to be a live actor, and it was when the attraction fist opened. He said the departments ended up axing the actor in the knight costume, not because of safety or guest concerns (as the guests generally loved it), but instead due to those respective department's budget concerns. So while the designers were sure to keep the knight inside the HM at WDW when it was designed, they didn't include the knight in the turret designs because it was their way of "making a subtle statement."
The funny thing about this story is that I never actually knew that there was an actor in the knight costume roaming the HM at Disneyland back in the 60's. In fact, I thought this guy was off his rocker at the time. Only after this guy telling me this story did I go do my research - and sure enough, there were entertainment actors who worked the attraction in the knight costume. It's even chronicled in a behind the scenes book on Disneyland complete with pictures of the actors doing their thing! Who knew? (I didn't LOL).