The two big drama series in the Sky Atlantic / HBO stable are both debuting on disc early in 2012. Season one of Boardwalk Empire finally comes out on disc on January 9th, a ridiculous 15 months after it debuted on HBO and a month after season two has finished. Those waiting for season one of Game of Thrones will be happier as that box set will be released just before season two starts - March 5th.
Why the long gap? I don't think it's anything to do with the Sky Atlantic deal as they've both been delayed stateside too. It's, more likely part of HBO's strategy with it's HBO Go service and the competition with NetFlix.
Season five of AMC's Mad Men is scheduled for the spring on Sky Atlantic by the way. The show may appear on online services such as iTunes as previous seasons have been available there immediately after UK airing.