> It seems to me that such an animal would be fragile and incomplete at best.

There's no reason for it to be either fragile or incomplete. My cross builds have a goal of being comprehensive.

> Python builds on OS X normally require certain OS X frameworks outside of those included with the compiler.

If the user supplies the Apple Mac OS X SDK then the frameworks are correctly detected and used. To enable this, I use a set of wrapper scripts to enable this, here's the contents of x86_64-apple-darwin11-gcc:

#!/bin/sh
# Auto-generated, do not edit
/home/ray/darwin-cross/apple-osx/bin/i686-apple-darwin11-gcc -isysroot /home/ray/darwin-cross/MacOSX10.7.sdk -mmacosx-version-min=10.5 -DMAXOSX_DEPLOYEMENT_TARGET=10.5 -m64 "$@"

> Why would we want to officially support this particular variant of cross building on another platform?

There's 3 separate issues merged into this patch, general cross compilation fixes, the new darwin cross compilation feature and a few darwin warning fixes (that apply equally to cross and native). I shouldn't have done that, and am in the process of splitting this issue up so that each part can be judged in isolation. Please see the new issue I've made for the general cross compilation issues: http://bugs.python.org/issue16292
..later I'll work on a new patch for this issue.