Microsoft Windows 8.1 reached RTM status a few weeks ago. At first, Microsoft said that MSDN and TechNet subscribers wouldn’t be able get the new ISO images and told us to wait until General Availability (GA) on October 18 like everyone else.
Windows 8 can be downloaded from almost anywhere but not everyone has the time or the will to check if they are indeed original, untouched images just like the ones from Microsoft MSDN.