Lots of ifs and assumptions - and we're still running development code.
I understand what you're saying, but MS is working on this as I previously mentioned.
It's not clear that the two things you mentioned (size of the System Reserve part and No-execute Memory Protect) are connected, but I'll take your word on that. It's possible that a different bug presented itself as the one you saw.
I'm confident that MS will release Win10 without major issues ... there will be issues that are already being addressed for two releases next year. And many known issues will have updates earlier. That's how development works.
Here's some reading material:
Windows 10 FAQ & Tips - Microsoft
Windows 10 Specifications - Microsoft
To install a 64-bit OS on a 64-bit PC, your processor needs to support
After skimming through the list, most of the CPU requirements seem to focus on 64 bit installs. I wonder if the issue you saw would present itself if you installed the 32-bit windows (I know.... you want a 64-bit install. It wasn't a suggestion, it was wondering)
Why are they requiring it now? To take advantage of the new features ... progress ... the future ... you know advancement