Ubuntu updates not consistent between systems

[edwardp-KK0ffGbhmjU at public.gmane.org]

I have Ubuntu 9.10 (actually, Xubuntu) installed on two systems, a 
desktop and a laptop.

The updater (on the laptop) indicated there were 26 updates last night 
and another 11 this evening.  The updater then proceeded to download and 
install the updates.  A few of them were CUPS-related.

On the desktop, before I manually ran it a few hours ago, it indicated 
it was last updated three days ago and there were no new updates, yet 
the settings show it is to check on a daily basis.

I have the same software installed on both systems.  Why would one 
indicate updates are available, while the other does not indicate the same?