There is a difference between how the .py files get installed and how the scripts get installed.
umask was 22.

The files have just read permissions as they sit in the distribution (source control makes them
read only unless you are changing them. But distutils is smart enough to make them writeable
in the build directory or a rebuild would die.

Here after an install is a portion of what is in the build directory:

build/lib/browser:
total 565
drwxr-xr-x    2 dubois   climate      1024 Aug  5 10:06 ./
drwxr-xr-x    3 dubois   climate      1024 Aug  5 10:06 ../
-rw-r--r--    1 dubois   climate        15 Jan  4  2001 __init__.py
-rw-r--r--    1 dubois   climate      2593 May 17 13:43 gui_about.py
-rw-r--r--    1 dubois   climate     50113 May 17 13:43 gui_alter_plot.py
...
-rw-r--r--    1 dubois   climate     57129 Aug  1 09:32 vcs_function.py

It is not smart enough to do this to the scripts:
build/scripts:
total 1108
drwxr-xr-x    2 dubois   climate      1024 Aug  5 10:06 ./
drwxr-xr-x    4 dubois   climate      1024 Aug  5 10:06 ../
-r-xr-xr-x    1 dubois   climate     61224 May  2 09:04 ASD.scr*
-r-xr-xr-x    1 dubois   climate      5150 May 17 13:43 HARD_COPY*
-r-xr-xr-x    1 dubois   climate       232 Apr  4 09:08 cdat*
-r-xr-xr-x    1 dubois   climate        90 Feb 12 10:58 cdatnews*
-r-xr-xr-x    1 dubois   climate       200 Apr  3 13:47 vcdat*
[dubois@almanac browser]$ 

After .py files installed, they have group write.

[dubois@almanac browser]$ ls -l /home/dubois/linux/lib/python2.2/site-packages/browser
total 982
drwxrwxr-x    2 dubois   climate      2048 Aug  1 09:42 ./
drwxr-xr-x   20 dubois   climate      1024 Aug  3 15:33 ../
-rw-rw-r--    1 dubois   climate        15 Jan  4  2001 __init__.py
-rw-rw-r--    1 dubois   climate       175 Aug  1 09:42 __init__.pyc
-rw-rw-r--    1 dubois   climate      2593 May 17 13:43 gui_about.py
-rw-rw-r--    1 dubois   climate      1332 Aug  1 09:42 gui_about.pyc
-rw-rw-r--    1 dubois   climate     50113 May 17 13:43 gui_alter_plot.py
-rw-rw-r--    1 dubois   climate     57129 Aug  1 09:32 vcs_function.py
-rw-rw-r--    1 dubois   climate     37090 Aug  1 09:42 vcs_function.pyc
[dubois@almanac browser]$ 

But scripts installed are not writeable:

[dubois@almanac browser]$ ls -l /home/dubois/linux/bin
total 3672
drwxr-xr-x    3 dubois   climate      1024 Aug  5 10:10 ./
drwxrwxr-x    7 dubois   climate      1024 Aug  1 09:42 ../
-r-xr-xr-x    1 dubois   climate     61224 May  2 09:04 ASD.scr*
-r-xr-xr-x    1 dubois   climate      5150 May 17 13:43 HARD_COPY*
-r-xr-xr-x    1 dubois   climate       232 Apr  4 09:08 cdat*
-r-xr-xr-x    1 dubois   climate        90 Feb 12 10:58 cdatnews*
-r-xr-xr-x    1 dubois   climate       200 Apr  3 13:47 vcdat*
[dubois@almanac browser]$ 

This causes an error if I change cdatnews, for example, and try to reinstall. 
It happens in either the build directory or where I install it.

copying Scripts/cdatnews -> build/scripts
error: build/scripts/cdatnews: Permission denied
[dubois@almanac browser]$