To have them listed in package managers you'd need to add the source
to the repositories and in general this isn't as secure as keeping to
the ones installed as standard. Not all repositories are maintained in
a strict manner and can have rogue packages that do more than they say
they do. It was a 3rd party repository that was responsible for the
last trojan horse download - ostensibly a screen saver - which was
soon jumped on by the Ubuntu community but it does show that users
still need to be careful where they download stuff from even with
Linux !!

Sticking to the main Ubuntu repository means all packages have been
carefully vetted and checked before being released for download and is
by far the safest course of action. Many of the lesser repositories do
not fully check packages that are uploaded to them so if using these
it's vital to know how to harden Ubuntu and also be able to monitor it
for suspicious activity.

MC> None of the so called package managers I have, have ever search
MC> detected any package I have downloaded. They seem to all only work
MC> with the original distribution packages.