They did release it for the windows XP 64bit editions for AMD64. So no it was definitely released, it has rendering issues but it is there and works AFAIK. As best I can tell it was removed because it didn't fit vista's aesthetic not that they couldn't get it to work.

Because if MS had that agreement... almost nothing would have been released on AMD64 as very little actually made it to IA-64 or was supported there realistically.