The file src/bin/sage-bdist contains a mistake:
'ARCHES' should be 'ARCHS'.
The effect of the mistake is that the OS X application is always
built as 32-bit ('i386').
This can be seen in the OS X 10.9 .app version
currently being distributed officially, by running
$ file
Sage-6.3.app/Contents/MacOS/SageEverything in sage/local/{bin,lib} is 64-bit, so the mistake
probably has no significant effect on the running of sage code.
Daniel