Someone correct me if I am wrong, but I am about 99% sure that M$ has to individually sign ever driver for 64-bit windows.
therefore it is M$'s fault!
I'll correct you.
Apple first must provide Microsoft the 64-bit iPhone driver to digitally sign, which they have not done. So until Apple provides MS a 64-bit iPhone driver, it is Apple's fault the iPhone does not work on MS 64-bit operating systems.
Now, considering the number of iPhone/iPod users at Microsoft, maybe MS will just write the driver themselves, but they will need Apple's permission to release it. So until Apple gives that permission, it is still Apple's fault.
Only until Apple delivers MS a driver and MS takes their time to digitally sign it will it then be Microsoft's fault.