Administration menu or admin_menu should be in core.
To substantiate, one needs to download and install both the above and the Drupal 7 dev version.
Admin_menu and the upper admin bar in Drupal 7 looks almost same but admin_menu is more nifty.
It gives direct and easy access to specific pages without the need for page scrolls or going through extra page loads. The Drupal 7 admin bar looks more like the standard left side menu which has been horizontalised and stuck at the top, with probably no option to unfix it if I want.
It can be argued that Site Configuration drop down can become longer when there are 100 modules but apart from system/core modules others can be left out then with just link to a page of contribs. The rest is easier and direct access, what an admin bar is supposed to be. It is also more descriptive and useful in certain areas like "Add new content" rather than "Add" which being non-contextual adds confusion at least in a few sections.
Personally I found no problem with the system that was in Drupal 6 but usability tests must have confirmed the need of the bar. If the bar has to be there I feel admin_menu should be there.