Are there any LEGO elements not being produced because of mechanical problem with the mould?
I've been wondering the reasons why a number of pieces are no longer available and it appears the decision to reduce the overall amount of different pieces is simply a cost based one.

From a Q/A with someone from the Lego Company:
"...the piece count has been reduced drastically and there's a move back to roots in Lego, not only for creativity but to save money. Lego went from 12,000 different pieces to 6,800 in the last few years-a number that includes the color variations."

snippet was from here:
http://lego.gizmodo.com/5019797/everything-you-always-wanted-to-know-about-lego