I recently tried the new Ubuntu release and when I wanted to change the cache setting of Ubuntu update, I noticed that the Synaptic Package Manager was no longer available.
Why? It was one of most useful applications in Ubuntu in my opinion.
You can read a short description about the reasons in the Ubuntu Wiki: https://wiki.ubuntu.com/SoftwareCenter#Rationale
Quote:
Early versions of Ubuntu shipped many graphical utilities for
installing and removing software: Add/Remove Applications, Synaptic
Package Manager, Update Manager, Software Sources, apturl, GDebi, and
Computer Janitor. This redundancy increased the amount of interface
people had to learn, wasted space on the Ubuntu CD, fragmented
development effort, and made people more likely to think that
unsanctioned software installation methods were safe. Ubuntu Software
Center replaces Add/Remove Applications, Synaptic, apturl, and GDebi,
and acts as the main entry point to Software Sources.
Beyond providing a central point for installing and removing software,
USC plays a small but important part in encouraging application
development on Ubuntu, by providing application developers with a
prominent way to offer their software for installation.
