I disagree with point #4. Frameworks need to make things practical. You can't just add something and tell the user to go change the settings on a GUI.
Even when reconfiguring via PHP is possible, doing so is dangerous and might make a PHP-illiterate user with his site offline without knowing what to do.
Besides, frameworks need to assume that web server configuration might not always be modifiable by the user, and even when modifiable it might not be modifiable without a GUI. So you NEED a PHP-based solution anyway and adding a solution that relies on server configuration iss to much trouble for it's worth when you could be working on a caching engine instead.
Of course some things only work this way when you use Apache. But that is what Rasmus is saying, frameworks want to make things flexible for settings that do not change at the runtime, like the Web server or the database server. That flexibility imposes a cost and is worth nothing for most developers.