this solution - which I assume is the same as the one with the link to installing 8.1 with a product key - DID WORK FOR ME. I did it from the installing 8.1 with a product key site ( http://windows.microsoft.com/en-us/windows-8/upgrade-product-key-only), and I did not create a USB stick but simply downloaded the extraction pack to my pc and ran it.
!! Thank you to Cyberium and rdunton who seem to have figured this out !!!
I would recommend NOT bothering with all the various (and fruitless) suggested machinations around trying to manually download missing updates, running the update troubleshooters, or running DISM or sfc /scannow, or whatever other time-wasting solution that's been recommended, because, as noted in this forum, none of those ultimately work. (Trust me, I tried them all)
Just swallow hard and believe that you needn't go through all that pain for 8.1 to work well once you've installed it. At least that was the case for me; and for installing from Windows 8 (not 7).
if you don't have an 8.1 key (I didn't) just call Microsoft live and complain bloody murder and IF you have an 8.0 key I will bet they will give you an 8.1 key (as they did with me).