While I am sure some of this is Obama trying to put loyalists into power, let us not lose sight of the fact that there were several major snafus with regard to our nuclear arsenal that took place later in the Bush Administration.
Some of these changes may be a result of the investigation that took place into those incidents.
The previous problems may be related, however it looks like Gates has his hands full..
http://groups.google.com/group/total_truth_sciences/browse_thread/thread/d58edcff9fbd02b0