Well, I may not have any info about the reason for the delayed release either, but I have read two quite disenchanting reviews and as a consequence cancelled my preorder.
Here is one:
http://www.adventuregamers.com/articles/view/18384 The "best" things could be summarized as the game being extremely simplified, no deduction, terrible mechanic puzzles that have no place in a Poirot adventure game and on top of already limited gameplay constantly being told what to do.
EDIT: what bothers me the most is the publisher's having marketed the game as being challenging which an adventure game where you play Poirot bloody well should be.
It appears another playthrough of Evil Under the Sun is in order which I can wholeheartedly recommend.