One of the problems on Ubuntu platforms is that the Software Update tool doesn't remove the old kernels after an upgrade, but the Ubuntu devs are now talking whether their tool should be used to perform this kind of cleaning.
It might seem like a trivial stuff, but if you're running an Ubuntu system for a long time and you never clean up, you'll end up with a lot of installed kernels. It can get to a point where you'll be looking to clean up the space on your home partition just to make a simple system update.
This is not really an issue for regular Linux users who also like to do various tasks in the terminal, and there is a simple enough command that can take care of this problem, but there are also beginners who don't know up from down and they won't know that it's even an issue.
Making Software Update to clean up the system is easy, but is it the right decision?
A user raised this issue on the mailing lists and developers are still discussing whether they should change how the Software Update should act. It's not difficult to make it behave the way they want to, but that is the precise question that needs to be asked. Do they want to? There are some conceivable scenarios where this might not be a good idea, but they have to weigh it against the other scenario, of running out of space from kernel updates.
This is an issue that's probably a legacy issue from Debian. If you want to clean your system, you can do it very easily from the terminal. Just run the following command (you will need to be root):