They patched this in because people complained about this going missing when they removed the ability to sort columns in about:config (beforehand you could “sort” the modified-column to have all modified fields appear at the top).
So, while you’re right, that’s probably more effort than they really wanted to put into this.
And if you do want to keep track of your modified about:config-preferences, you might rather want to keep them in a user.js-file anyways: http://kb.mozillazine.org/User.js_file
That way, you can also put it into version control and easily apply it to new Firefox installations.
They patched this in because people complained about this going missing when they removed the ability to sort columns in about:config (beforehand you could “sort” the modified-column to have all modified fields appear at the top).
So, while you’re right, that’s probably more effort than they really wanted to put into this.
And if you do want to keep track of your modified about:config-preferences, you might rather want to keep them in a user.js-file anyways: http://kb.mozillazine.org/User.js_file
That way, you can also put it into version control and easily apply it to new Firefox installations.