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.
That driver is blacklisted in 8.1 and Microsoft demands from the vendor to pull it from their homepage.
Why they haven't revoked the signature, I don't know (maybe it would break the driver in Windows 8 too?). But the above is apparently what happened.
what you've just done is disproved your entire hypothesis that WindowsRT doesn't support Ethernet.
That was never my hypothesis! Quite the opposite. My hypothesis was that WindowsRT DOES support Ethernet, and Microsoft is blocking it artificially. Others in this thread tried to construct a technical issue for this (Dahat: "if you took a little time you might quickly realize which kind of drivers work and which don't.").