Why are these 3 upgrades being held back and not upgraded?

arv@Workstation:~$ sudo apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages have been kept back:
gir1.2-cogl-1.0 gir1.2-coglpango-1.0 libclutter-1.0-0
0 upgraded, 0 newly installed, 0 to remove and 3 not upgraded.
arv@Workstation:~$

This is a minor complaint relating to a lack of information, and not a fault of the system.

Recently completed a dist-upgrade to Ubuntu 13.04.
Running Gnome Classic on AMD 2X64-3800 with 4GB RAM & 1TB HD

Thanks,