Technically, it's not a delay because Warner Bros. hasn't actually announced a home media release date. The February 5th date only came from retailers.
As for why June:
The HD Room
One of the trickier release dates to figure out has been Cloud Atlas. There is new evidence that suggests Warner Bros. will hold this film until June 11, 2013, possibly because of the lack of Academy Award nominations it received. The ambitious film would likely get lost in the shuffle amongst the previously mentioned titles.