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I think you are underestemating the importance of this.
You are of course right that it isn't the end of the world, but not having a well functioning menu editor is one of these little things that will annoy people to no end.
Just take a look at about every Linux related support forum and the amount of questions that were asked after Gnome 2.10 dropped menu editing altogether. I'm sure you'll find thousands of questions about this, as you are going to find thousands again about not being able to add something to the menu.
And who cares about tools for power users? Power users can edit the .desktop file themselves if they have to, someone who is not a power user, but who simply wants to add a menu entry can't.
To sum it up, this is one of those little braindead decision gnome devs seem to like to make from time to time, probably to keep us from getting to enthusiastic about Gnome.