Ahh, just realised that you can buy the case on its own from HP, interesting decision on their part! The other point still stands, are you having problems finding such a board? Basically any high end mATX board would do what you need.
That said, the case appears to be £550 from what I can see which is a ridiculous amount for a case like that, apart from being at an angle, it doesn't really look to be anything particularly special. Don't get me wrong, I'm not the sort of person that tells people to buy the cheapest case possible, I strongly believe that you should get a good case however I can't see what makes that worth remotely near the price they are asking.