From what I read, Accenture built the system using SQL Server 2000... but this was a system that had been upgraded in 2007. Why didn't they use SQL Server 2005?

From what I read, Accenture built the system using SQL Server 2000... but this was a system that had been upgraded in 2007. Why didn't they use SQL Server 2005? I tried looking around also but couldn't find anymore technical details on what exactly caused the system to fail. I should mention that despite being a .Net guy by trade I too would recommend a Linux system for something like this, especially for performance reasons where microseconds matter. Still I can't help but feel a little frustrated that no one ever said what exactly occurred beyond "one or two unforseen events happened that brought down the London exchange for several hours". In fact, one article even attributed the outage to human error! Aside from poor UI design or confusing procedures, sometimes it's a matter of PEBKAC. (or maybe I just didn't get lucky in my searches)