Apparently these drivers mentioned in the linked post work without any problems.
Wait... so if the drivers work, what's the problem!? The limitations in WindowsRT are to do with driver signing requirements, so if you've found a way to get Ethernet to work via a driver in one of your links on WindowsRT, what you've just done is disproved your entire hypothesis that WindowsRT doesn't support Ethernet.
If Microsoft don't like your driver, they don't "ask you to remove it" and then cry when the drivers leak online. They just revoke the signature for the driver and then it wont load any more.
Hence we can conclude that by the very fact that you have yourself demonstrated a clear example of a USB to Ethernet device which is Microsoft signed and loads on WindowsRT, we can see that all the rest of this thread is mainly utter nonsense.