Oh, I now understand why I feel guilty, I proposed a patch rewriting getstatusoutput() in the issue #10197. My patch ends with:

+    if os.name != 'nt':
+        # convert status to be interpreted according to the wait() rules
+        sts = sts << 8

This fix is that simple, but it means that depending on the Python version, you will get a different status...

Python 3.3 doesn't accept bugfixes anymore and so cannot be changed.