it's been some years since I've used aptitude (apt-get is more to my liking and is the recommended on my distro), so I don't remember exactly how to interpret that output. However I can think of a couple of reasons:
- You have some packages on hold. To check you can run:
aptitude search "~ahold" | grep "^.h"
- You need to do a "aptitude full-upgrade" (new packages to install)