It has been INI_ALL for a looong time until somebody decided to set it
to INI_SYSTEM.
Actually it was "--enable-url-fopen" for a loooooong time until it became
runtime configurable. It was *mistakenly* set to PHP_INI_ALL, but was
supposed to have been PHP_INI_SYSTEM. (In line with prior behavior)
As I posted earlier, url_fopens *can* already been temporarily disabled and
reenabled using stream_wrapper_unregister() and stream_wrapper_restore().
There's no need to make the .ini setting magic by making it disablable
one-way.
However, as Derick pointed out php_admin_flag can be used to override the
changability and keep it a system-wide setting on a site specific basis,
so while there's absolutely no reason to make it PHP_INI_ALL, I can possibly
buy into it providing the change happens in HEAD and nowhere else. There's
no reason to break this setting in a stable branch, especially one as old as
4.3/4.
-Sara
P.S. - This was discussed at the time the change was reverted back to
PHP_INI_SYSTEM.