This is entirely wrong. Microsoft calls it "amd64" for the same reason that everyone calls amd64: AMD developed it at a time (~1999) that Intel had convinced itself that its 64-bit future was with Itanium, not x86. It was not until Intel's Yamhill project (~2003) that Intel ceded to AMD's ISA lead (and Itanium's relative failure in the market) and... implemented amd64. But by then, every operating system had support for AMD's architecture -- and the ISA's name was not up for renegotiation.