Looking at the write-up on the frontpage, it says: "Considering we haven’t gotten official pictures yet, I’d reckon this is an accidental early release. It was slated for August 2012, and is rumored to be a retailer exclusive."
I don't actually believe it is an accidental early release. Here in Europe (well, at least the Netherlands), the Summer wave of Star Wars sets have ALL hit retail as of this Monday, the 28th. And German T'r'U stores had these new sets over a week ago.
I think Lego is just following another staggered release of sets, due to production and marketing issues (they've probably realised it's better to seperate the release of popular new waves of sets by several months). TLC have released the LotR sets in the US in May, while Europe is scheduled to get these in August, while doing the exact opposite with the Star Wars sets (i.e. releasing them in Europe starting from late May, while only releasing them in the US from late July / early August). There's no reason to delay the European release of Palpatine's Arrest until August: releasing it in two months time would have it contend with the LotR sets, without the benefit of a whole SW wave push.
Anyhow, there seems to be some negativity about this set. Even though I am totally averse to the Prequel Trilogy movies, I do like this set quite a lot. Good figures, without ugly Clone Wars style faces, in a nice playset with a cool little craft. I most definitely wouldn't buy it at the current €-price, but at discount, I'd find a place for it no problem.