I'm sure this has already been called to your attention, but I will
email anyway.
It appears that the x86 LiveCD ISOs have been maximized in size so that
they can _just_ fit on a standard CD. However, the x64 ISOs simply
contain the same packages with the different arch, but are larger
(presumably due to compatibility libraries, binary size, and such).
This makes them too large to fit on a single CD.
Matthew