The issue is the way that the position of the icons is set by the user. By default, gnome sets the left-most icons to negative numbers as a position, and the right-most icons to some very high numbers. When a user clicks and drags their own applets to the panel, they are considered absolute positions and set their position in pixels.

The fix would involve an overhaul of the interface used to add icons to the panel, and it would not fix any existing panel configurations. It would also require at least some sort of an extra step of understanding for the user (Do you mean left justified, right justified, or absolutly positioned?) and some interesting Gnome-panel rendering hacks.

This is a lot of work for something that doesn't affect a lot of users, as most users do not customize their panels, and of those that do probably are not changing their resolution often. If someone who wanted to work on user interface hacking worked on other parts, such as improving file system access, preferences configuration, or even login screens, it would be more appreciated by more users.