The upgrade for $14.95 is for the qualifying Win7 PC only.
Similarly, you can get the upgrade for $14.95 for a qualifying Win7 PC purchased after sometime in June (I don't recalll the date). You are not required to use the upgrade on that PC, though. It's legitimate to use it on a different PC.
You can make a ISO:
Windows 8 Upgrade Assistant - Download and Run
When downloading the upgrade you need to
If you need to download 32bit Windows 8, download from a 32bit PC.
If you need to download 64bit Windows 8, download from a 64bit PC.