Take a look at the monthly market share stats for Windows and you’ll see a good proportion of Windows 8.x users are still on the original version of the tiled OS. For some it’s a matter of choice, for others it’s because they simply can’t update to Windows 8.1.
A large number of users have experienced the dreaded Blue Screen of Death when attempting to perform the update to Windows 8.1, which has resulted in them being unable to complete the process. Fortunately, Microsoft has a patch to address the issue.
The fix, which is still in testing in "select markets" reportedly solves the problem and allows Windows 8.0/RT 8.0 users to (at long last) complete the upgrade.
"This [Windows RT] pilot program is an example of ways we're experimenting to help ensure more of our customers benefit from a continuously improving Windows experience," a Microsoft spokesperson told Paul Thurrott. "Similar to how the Windows 8.1 Update  process works today, the pilot program will automatically update consumer Windows 8 and Windows RT machines for free to Windows 8.1 Update and Windows RT 8.1 Update in select markets".
If you’re one of the affected customers, keep checking Windows Update for the fix. Thurrott points out the RT version of Windows 8.1 can be downloaded from the Microsoft Support website and installed manually now. Windows 8.0 and Windows RT 8.0 users will first need to install update 2871389 before applying the Windows 8.1 update.