wxPython does in fact work across both platforms. All praise to vendors (such as Netherworks and Semidieu/ShaderWorks) who are building scripts with wxPython these days. 

We all know that the version of tKinter-based Python used by Poser 9 / 2012 is not compatible with older compiled tKinter-based scripts. It turns out that even if these old scripts are updated, many of them still won't work with 64-bit Macs running Poser 9 / 2012. Even dumbing down Poser Mac to run in 32-bit mode does not help; Poser immediately becomes unusable and its menu commands are removed when trying to use these tKinter scripts in 32-bit mode.

A lot of wonderful scripts will fade away, at least for Mac users, unless someone rewrites them for wxPython. Their original authors do not seem inclined to do so. And since they were free, it's hard to complain about it.