Delighted to see that that Microsoft has changed the rule for Win7... I thought they might but I wasn't really sure (these days Microsoft is anything but logical it seems.) With the technet/MSDN upgrade, the only way to seamlessly go (by that I mean without losing *any* installed programs or files) from Win7 to 8.1 was to first upgrade to 8.0 and *then* upgrade 8.0 to 8.1 with the full 8.1 RTM iso (I never bothered with the preview, really, except to play around with it on a separate partition.) That's what I did--bought 8.0 for $39.99 back in January from Microsoft, and then installed and upgraded to 8.1 from the full MSDN 8.1 RTM .iso. No problems at all--smooth sailing. All 8.0 programs transferred without difficulty to the 8.1 RTM install.
So it appears the code ban on allowing a Win7-8.1 RTM .iso upgrade was temporary after all, and only limited to that ~one-month period between putting the 8.1 RTM .iso on MSDN & Technet and October 18th, when the 8.1 RTM iso will be officially available to everyone. IE, Microsoft didn't want anyone who had not bought 8.0 earlier to be able to use the 8.1 RTM iso upgrade prior to Oct. 18th. This may be a good sign that Microsoft is beginning to come around. We'll see.