They need time to create a solid demo, bug check it (again, just a freakin' demo), submit it to Sony for certification, and leave time for any possible error throughout the process.
Submitting a demo takes over a month to Xbox or Sony.
This is the same process it has always been.
If you would like to see a 100% true accurate representation of the demo, you'd see it after the game was released. And in this industry, that does not do anything for sales.
The demo released was to give you a glimpse on the major gameplay mechanics introduced this year. Look through the forum at all the discussion, people asking for tutorials, etc.
Can you honestly say it didn't do it's intention?