Can anyone tell me why are the keep moving the releases? now it stands of 5-17-2011 and another site says 158 days. Is there any reason to explain?

AFAIK they haven't announced a release date yet. All they've said is spring 2011.

If you're reading it off of anything but the official site I wouldn't trust it.

As has been said many times before, Not to mention http://www.gamesas.com/index.php?/topic/1160885-release/ not half way down the first page of the forum.
Any release date found in places like Online stores are simply unofficial place holders set by the site so that Pre orders have a date.

But until an Official release date is released. Spring 2011 is all we get.
As also said in the http://www.gamesas.com/index.php?/topic/1113952-brink-faq/ as well

If you wish to discuss it please use http://www.gamesas.com/index.php?/topic/1153147-lets-see-how-many-different-release-dates-we-can-find-for-brink/

Can some1 please lock this thread

Question answered. As of yet it's 'spring 2011', and we can safely assume that when it's finally a solid date, Bethesda will make an announcement.