Minor nitpick: the default GUI toolkit for Python is Tkinter, not wxWidgets. Both toolkits come standard with Tiger, though neither one comes with previous versions of OSX.

Tkinter is a Pythonic wrapper around Tk, the default GUI toolkit for Tcl. Tk has two main advantages: it's very simple to hand-code a GUI in it, and it's been ported to many scripting languages. It's the default in Perl and Ruby, for example, and there's even a version of ksh that lets you write GUI shell scripts.

This is not to say that I encourage developing apps in Tk. Many GUIs are not hand-coded these days, and if you don't use a language to which Tk has been ported then that advantage also disappears. It's also extremely bare-bones by modern standards; although you have all the basic GUI elements -buttons, menus, frames, and so forth- you don't get anything like tabs, combo-boxes, or other advanced GUI elements which we take for granted nowadays.