Yes and no. There have been some cool projects for Rails that provide administrative interfaces, but they all suffer from a lack of critical mass. Django's admin interface is just core to the framework - not because it has to be, but in the way that the core team sees it as something that can't languish.
Being a part of the framework itself makes the Django admin interface always receive attention. Separate Rails projects do exist, but are often by one or a small number of people and not as widely used as the Django admin interface. So, they are there, but often don't have quite the polish and utility of Django's interface.
On the horizon, merb-admin is being ported to Rails 3 by Yehuda Katz (http://yehudakatz.com/2009/12/31/spinning-up-a-new-rails-app...). If that comes to fruition, I think it might become a standard tool for Rails users who want admin pages. We'll see.
Being a part of the framework itself makes the Django admin interface always receive attention. Separate Rails projects do exist, but are often by one or a small number of people and not as widely used as the Django admin interface. So, they are there, but often don't have quite the polish and utility of Django's interface.