To use a more neutral name is really a good thing IMHO.
I'm just a lowly user so I can't comment on the technical aspects of the name decision, but IMHO the 'AMD64' name is a much better public face to the project - it is immediately obvious what it means: faced with the ports page, someone who has just bought an AMD Athlon64 processor is going to be much happier with this than x86[-/_]64 which
is more of a history lesson than a name, and doesn't square with the existing naming scheme, as has already been mentioned. Plus I thoughtthe Intel 64-bit Prescott extensions weren't going to be entirely compatible? In this case, company-specific extensions are essential.
Matt