Starting Python script without explicitly having X11 open
If I had to guess (and I do...), it sounds like you installed an X11 based version of python and tkinter rather than one that uses the native windowing system on OSX. I think you can safely write your scripts without telling people they have to have X11 running. You merely have to say they have to have a proper environment set up -- either a native version of python+Tkinter or have X11 running and have an X11-based version of python+Tkinter
In other words, this isn't a regression in python that you have to code around, it's just a side effect of your particular installation of python.