IMVU's downloadable client is built atop CPython.  80% of our users use 32-bit Windows and 20% use 64-bit Windows.  We do not intend to provide 64-bit builds of our application for many of the same reasons sketched out in http://blogs.msdn.com/b/ricom/archive/2009/06/10/visual-studio-why-is-there-no-64-bit-version.aspx

Process address space is one of our key bottlenecks: limiting the amount of cache we can mmap in, various runtime heap reserves, etc.  For those 20% of users running 64-bit Windows, /LARGEADDRESSAWARE would give 32-bit Python access to 4 GB of address space, which would certainly help them.

The other reason not to use 64-bit binaries is that they consume significantly more memory and cache, especially because Python is so pointer-heavy.

In the meantime, we can use editbin /LARGEADDRESSAWARE to modify the shipped .exes.