The file associations are actually part of the launcher, which *technically* is independent of the Python install it is bundled with. So it doesn't have any references to the Python install directory, and double-clicking Python files with shebang lines will work properly.

For 3.5.1 I'm considering making the launcher an independent uninstall item (in response to another issue), so if you install 3.5.1 and then remove it, you can keep the launcher. For this to work, it has to be independent of the main install, so it can't refer to the DLLs directory.