I completely agree with Luvtoy. This is the reason, and not for marketing purposes. It's propostorous that anyone would even suggest it, and actually believe that's why it's delayed.
Some people are obviously too stupid to realise games take a bloody long time to make, and even when finished, take a bloody long time to test, and re-test, and re-test, to make sure there are no bugs.
Just next time you think that it was delayed for marketing, go and look up "Video Game Design & Creation" in Google. Save some time.